ASWORG/87 – 1
	1 April 1944.
	RESEARCH REPORT 27
	ANTI-SUBMARINE OPERATIONS BY CVE BASED AIRCRAFT.
	ABSTRACT
	A detailed study of A/S operations by CVE based A/C covering the period March 1943 to February 15, 1944 is presented. Included are limited data on CVE operations: the Task Group; convoy coverage; U/B search; effect of weather and sea conditions; A/C handling and storage; speed and endurance of A/C; communications; armament; a typical day’s flight operations; details pertaining to U/B sightings; the attack; coverage and effectiveness of search plans and sweeps. A tabulation of the results is given in Table I. The dependence of surprise on altitude is quite marked, although there is no appreciable gain in probability of sighting with increasing altitude. CVE based A/C coverage is such that on a single sweep there is, on the average, a 50-50 chance of sighting a surfaced U/B which is present somewhere within the limits of visibility as viewed from the A/C.
	-1-

ASWORG/87 – 2

1 April 1944.

INDEX
	Abstract		1
	Table I. Summary of Sighting Statistics		3
PART A
	Introduction		6
		The CVE's general features	9
		Launching and landing planes	9
	Operations
		The flight deck	10
		Factors limiting operations	12
		Other A/S equipment with the task group	20
		A typical day’s Flight operations	21
PART B
	Operating statistics		23
	U/B sightings by CVE borne A/C		23
	U/B trim at time of sighting and cause of sighting		27
	Factors governing degree of surprise in making
		attack	29
	U/B response to attack		31
PART C
	Effectiveness of CVE based A/C search		33

-2-

ASWORG/87 – 3

1 April 1944.

TABLE I
SUMMARY OF SIGHTING STATISTICS
Number of occasions when A/C sighted U/B					58
	Flying search			48
	Flying A.E.P. #15			4
	Investigating HF/DF			1
	Flying to relieve			2
	Mission not known			3
Number of U/B’s sighted					68
	Fully surfaced			53
	Diving trim			9
	Breaking surface			4
	Periscope depth			1
	Submerged			1
Number of U/B’s attacked					60
	Complete surprise to U/B			28
	Resulting in:	10A, 4B	50%
		3D	11%
		3E, 6F, 2G	39%
	Partial surprise to U/B			22
	Resulting in:	2A, 7B	41%
		4D	18%
		2E, 3F, 4G	41%
	No surprise to U/B			10
	Resulting in:	2A, 3B	50%
		1D	10%
		2E, 1F, 1G	40%
	TOTAL			60
		14A, 14B	47%
		8D	13%
		7E, 10F, 7G	40%
Evasive action - first attack				31
	AA fire		25
	Crash Dive		6
No evasive action – first attack				29

-3-

ASWORG/87 – 4

1 April 1944.

TABLE I. (Continued)
	U/B sunk as a result of first attack	8
	U/B not seen after first attack	6
	U/B crash dive after first attack	18
	U/B remained surfaced – AA fire	28
Number of U/B’s escaping attack			8
	While A/C engaged with another U/B	6
	By crash dive	2
Number of CVE cruises			24 ½
Number of CVE days in U/B waters			680
ABD assessments per cruise			1.5
ABD assessments per day			0.053
Number of plane-hours flown			34,700
Number of plane-hours per sighting			600
Number of plane-hours per sighting
	for land based planes in Bay of Biscay (1943)		101
Number of plane-hours per A or B assessment			1,240
Number of plane-hours per A or B assessment
	for land based planes in Bay of Biscay (1943)		1,390
Average visibility in miles			12.3
	For complete surprise	12.2
	For partial surprise	12.9
	For no surprise	10.4
Average altitude for sighting surfaced U/B			3,350
	For complete surprise	4140
	For partial surprise	2860
	For no surprise	2000

-4-

ASWORG/87 – 5

1 April 1944.

TABLE I. (Continued)
Average sighting distance for fully surfaced U/B					7.8
	For complete surprise			7.9
	For partial surprise			9.6
	For no surprise			4.7
Number of fully surfaced U/B’s sighted by wake					25
Number of fully surfaced U/B’s sighted by hull or C/T					27
Average state of sea for sighting surfaced U/B’s					1.9
	Sea state	0, 1	18
	“ “	2.	11
	“ “	3.	15
	“ “	4.	11
Average altitude of sighting partially surfaced U/B					2160
Average sighting distance for “ “					4.0
Average state of sea for sighting “					2.4
Average value of lateral distance W/V for surfaced U/B					0.38
Average value for W/V for partially surfaced U/B					0.26
Average distance from CVE to U/B					53.6
Average speed of U/B (in knots) at sighting					10.0
Average bearing of U/B relative to A/C				4^0 to port
	23 sightings to port, average angle of 65^0
	25 sightings to starboard, average angle of 47^0
	6 sightings dead ahead

-5-

	ASWORG/87 – 6
	1 April 1944.
	PART A
	INTRODUCTION
	Returning from a late afternoon patrol on 28 April 1943, a TBF from the USS BOGUE sighted and attacked a U/B at latitude 45^023’N, longitude 27^026’W. Although the U/B escaped without leaving evidence of damage, this action was the curtain raiser for a long series of actions between CVE based planes and U/B’s which have contributed materially to the great loss of effectiveness of U/B warfare in the mid-Atlantic.
	In all, 60 U/boats were subjected to attack between March 1943 and 15 February 1944 by CVE-based aircraft alone. Numerous other U/boats were attacked by the CVE’s escorts, sometimes alone, sometimes coordinated with aircraft. Not only has the U/boat activity decreased but those that remain have become exceedingly wary. U/boats are now spending less of their time on the surface during daylight in the mid-Atlantic.
	As a single example of what this victory has meant to our supply lines, consider the case of the UGS and GUS convoys to North Africa and the Mediterranean. These convoys operate in the mid-Atlantic and since May 1943 have been covered or supported by the CVE Task Groups. During this period to the end of 1943, 2237 merchantmen crossed the Atlantic in UGS and GUS convoys. Only one of those ships was lost due to U/boat action. Not another ship was damaged by this cause. Contrast this with 26 U/boat kills by CVE-based A/C alone during the same period.
	The CVE with her screen of 3 or 4 destroyers (recently raised to 5 destroyers) composes a Task Group, assigned to ASW in the Atlantic. The main purpose of the Task Groups is two fold: (1) to provide aerial coverage for Task Forces escorting convoys, in order to protect the convoy from U/boats approaching on the surface, and (2) to search out and destroy enemy submarines. Incidental to this is the interception and capture or destruction of enemy surface craft, particularly blockade runners.
	The great success of CVE’s in ASW operations is due to their ability to bring both F4F fighter planes and TBF
	-6-

	ASWORG/87 – 7
	1 April 1944.
	bombers directly to the heart of the U/boat concentrations. The CominCh Daily Estimates of U/boat positions have proven most reliable in predicting the location of these concentrations. Initially, the presence of planes in the mid-Atlantic was such a surprise that the U/boats were a long time in getting over it. In nearly half the attacks the U/boats were so surprised that they were not able to fight back until after the initial attack was delivered.
	Customary procedure is for the CVE to be with the convoy while passing through areas where U/boats are suspected. While in areas where no U/boats are suspected, the Task Groups will leave the convoy and head for concentration areas, there to conduct offensive sweeps. As the situation developed, with U/boats molesting convoys less and less, the trend was to spend an increasing proportion of the time on offensive sweeps.
	For protection of the convoy and of the Task Group when away from the convoy, Aerial Escort Plan No. 15 or a slight modification of it is used. So tight is this plan that a U/boat surfacing within 25 or 30 miles of the convoy will be sighted within half an hour at the most, and on the average within 15 minutes of the time of surfacing. Likewise it would be unusual for a U/boat to be able to move in on the surface to closer than 20 miles. In general, a surfaced U/boat would be sighted by the A/C before he can get close enough to the convoy to sight it. The fact that only one ship out of 2237 was attacked bears testimony to the effectiveness of Plan 15. On offensive sweeps large areas can be swept over in a day. A single CVE has put as many as 51 planes in the air in one day. A track chart for these planes would include an area of 18,500 sq. mi. within one mile of one of these tracks and an area of 90,000 sq. mi. within five miles. This means that any U/boat in an area equal to the combined areas of Connecticut, Rhode Island, Massachusetts and New Hampshire would have a plane pass within a mile of it, and any U/boat in an area half the size of California would be passed at less than five miles.
	The plans for offensive sweeps vary from ship to ship. However, they all possess the general common characteristic that different fighter-bomber teams each cover a given radial sector. The planes fly radially out from 40 to 100 miles (depending on plan used) then fly a cross-over of 10 to 30 miles, then directly in along a radius to intercept the CVE.
	-7-

	ASWORG/87 – 8
	1 April 1944.
	This plan might be better understood if one uses the analogy of movement out along the spokes of a wheel. The CVE is the hub, a team composed of a TBF and an F4F will sweep out the area enclosed by two adjacent spokes and the portion of the rim joining them. The motion is out along a spoke to the rim, then along the rim to the next spoke, and in along it. The area covered also includes that immediately outside the spokes and rim.
	Having once established contact with a U/boat the fighter bomber teams swing into a coordinated attack, at the same time breaking radio silence to give the CVE range and bearing of the action. The F4F goes in first for a strafe. The purpose of this is to distract the U/boats gun crews and thus enable the TBF to press home a low altitude depth charge attack without being shot down. The TBF follows close in behind the F4F but usually at an angle to its course. Except for the rarely encountered AA boats, the U/boat is no match for the F4F’s fire power. Prisoners of war have expressed their great fear and general feeling of hopelessness after being submitted to their first strafing from an F4F. The usual consequence of a single strafe or a series of strafings is the shooting up of both the guns and the gun crews, setting the ready box on fire, and puncturing of oil tanks, so that oil leaks out. A sufficient number of F4F’s are not always available for making the sweep, in which case the TBF is alone.
	While the initial attack is being carried out, the CVE is sending an attack group of F4F’s and TBF’s to the scene. Aircraft from adjacent sectors are also directed to teh scene. The attack group is always standing by in a state of readiness while the patrols are out on a sweep. They are launched and to the scene in a matter of minutes, providing the CVE received the attack message clearly. Communications failures are disastrous at this point so a careful checkup on equipment is made as soon as patrol planes get into the air. If the message is promptly and clearly received actions even as far as 100 miles away can be reached by the killer group within half an hour of receipt of the message. Shorter trips are made in correspondingly less time.
	Once the U/boat has been sunk or otherwise forced under, surface craft are sent to the scene (unless other extenuating circumstances make such a move impracticable) and hold-down and gambit tactics are entered into. It was just such an activity that led the USS BORIE to her famous action with U/boats. Such coordinated action of fighter and bomber,
	-8-

	ASWORG/87 – 9
	1 April 1944.
	patrol planes, and killer groups, aircraft and surface craft, has resulted in the high ratio of kills and damaging attacks.
	The CVE’s General Features
	The CVE’s of interest to this study are: the USS BLOCK ISLAND – CVE 21, BOGUE – CVE 9, CARD – CVE 11, CORE – CVE 13, CROATAN – CVE 25, GUADALCANAL – CVE 60, and SANTEE – CVE 29. The SANTEE is a converted oiler of about 24,000 tons displacement, overall length of 552 feet, 75-foot beam, draft 18 feet and a speed of 18 knots. Except for the GUADALCANAL, the others are constructed on the Maritime Commission Mercantile hulls, having a displacement of about 14,300 tons, overall length of 500 feet, 69 foot beam, draft 25 feet, maximum speed of 18 knots and an economical speed of 12 knots. The flight deck and gun sponsons have increased the overall beam of the CVE’s to about 110 feet. The flight deck on the SANTEE is about 500 feet long and 85 feet wide, whereas the others have a flight deck about 440 feet long.
	Launching and Landing Planes
	The first planes off are catapulted. The catapult officer directs the pilot, “reving the prop”, “checking the flaps”, and so on. When the plane is ready and at the moment the pitch of the ship is correct the plane is catapulted. The deck runs are more difficult as it is desirous to take off just as the end of the deck is pointing up, rather than down. This means that considerable judgment must be exercised in starting the plane off at the right moment. Also because of pitch part of the run must be made up hill. The runs are only about 450 feet, yet usually the planes leave the deck before reaching the end of the run. The planes are just above stalling speed as they leave the deck. On rare occasions one stalls into the water.
	Following the launching the planes are respotted. The ATTACK GROUP is put in position for launching, one plane being on the catapult. Other planes that need to be turned up, or have the wings tested are also spotted where they can be worked on. In case one of the planes just launched needs to return for an emergency landing – and this happens frequently during the early part of the trip before the planes have all the “bugs” worked out of them – it will be necessary to respot all of the planes that have just been spotted. The planes must be placed in the area forward of the barriers leaving the landing strip clear. After the emergency landing has been made, the planes are again respotted.
	-9-

	ASWORG/87 – 10
	1 April 1944.
	When all is in readiness for the landings, the flag signals go up and the bull horn is sounded. The first plane approaches the carrier in a long flat glide from the port quarter. AS it comes up astern of the carrier it is under the direction of the signal flags in the hands of the air landing officer, who is located on a platform on the port quarter of the landing strip. The pilot cannot always see the deck as he gets near to it. He relies on the guidance of the air landing officer, who is a pilot of extensive experience. If the landing signal officer is not sssatisfied with the manner in which the plane is coming in, he will give it a wave off.  If the landing officer is satisfied with the plane’s approach, he continues to bring him in, and at the proper moment signals the pilot to “cut”. As a result of the cut the plane settles onto the deck. The tail hook picks up a pendant of the arresting gear and the plane is usually stopped within the next 50 to 80 feet.
	The actual landing is rather spectacular. The plane is coming in at very nearly a stalling speed. Slip streams from the ship have a marked effect on the plane. On some of the landings the planes come down rather hard. Tail wheels flying through the air are not an uncommon sight, and on rarer occasions a tire blows or landing gear collapses, and the plane skids along towards the side of the ship.
	After landing on the deck the plane is under the control of the deck officer. His crew rushes out, disengages the hook from the pendant and sees that the latter goes back into the plane. The pilot moves his plane according to the instructions signaled to him by the deck officer. In the case of the F4F’s the crew folds the wings. Wing folding on the TBF’s is automatic. The crew runs along with the plane to help push it around. All this action takes place rapidly and with fine coordination. After all planes are landed they are spotted and refueled. Those that are not needed above are taken below to the hangar deck – if there is room for them.
	OPERATIONS
	The Flight Deck
	The CVE’s originally carried F4F’s, SBD’s and TBF’s, but after a short trial the SBD’s were replaced by TBF’s.
	-10-

ASWORG/87 – 11

1 April 1944.

The TBF’s were considered superior to SBD’s in the attack because of the additional armament carried by the TBF’s and because the SBD’s wings do not fold, (hence occupying more space). The USS SANTEE carries a nominal complement of 20 TBF’s and 12 F4F’s. The other CVE’s have a nominal complement of 12 TBF’s and 6 F4F’s. These numbers vary somewhat from cruise to cruise but are fairly representative of a normal complement.

        Some data pertaining to flight deck operations for the SANTEE are given in Table II. It is to be remembered that the flight decks for the other CVE’s are about 11% shorter. A plan view of the flight deck is given in Figure 1 and 2.

TABLE II
Length of flight deck			500 ½ ft.
Width of flight deck			85 ft.
Length of forward parking area.			106 ½ ft.
Length of usable parking area while
	planes are being catapulted		309 ½ ft.
Length of landing area aft of barriers			309 ½ ft.
Maximum stretch of barriers			30 ft.
Maximum stretch of pendants			145 ft.
Spacing of pendants		24 ft. to 29 ½ ft.
Number of pendants			9
Barrier breaking strength			92,400 lbs.
Pendant cable breaking strength			46,000 lbs.
Minimum wind velocity for
	full-load runway takeoff		25 kts.
Minimum wind velocity for
	catapult launching		16 ½ kts.

-11-

	ASWORG/87 – 12
	1 April 1944.
	Factors Limiting Operations
	There are numerous factors which limit operations from the CVE. Aside from the military situation of the moment the most important are:
	1. Weather and sea conditions.
	2. Number of planes available.
	3. Plane handling and storage.
	4. Speed and endurance of planes.
	5. Pilot and observer fatigue.
	6. Communications.
	7. Armament carried by planes.
	8. Detection equipment.
	1. Weather and sea conditions. The effect of these elements on U/B sightings and attacks will be treated later on. However, the effect of weather and sea on launching and landing is worthy of discussion here. Landings are hazardous in a dead calm as the CVE is then barely able to produce the minimum wind velocity necessary for safe landings. The F4F’s in particular come in with such high speed relative to the deck that either a tail hook or a pendant may be severed. The TBF’s are liable to drop too suddenly at these low speeds and damage either a wheel or the landing gear. These hazards are usually considered minor.
	More hazardous are the conditions of a sea state of 4 or more combined with sharp, gusty winds. Here, one might have a serious accident because of a combination of deck rool, or pitch and a sudden change in wind speed. A rolling, pitching deck is hazardous for either launching or landing when strong, gusty winds are present. The plane is liable to get out of control on launching and to crash on landing. These operations are quite difficult for a sea state of 5, and nearly impossible for a seastate of 6. These conditions naturally cut down on the speed with which the deck crews can handle the plane. Worst of all is the case where icing conditions are added to the above. Here it is not unusual for the plane to go skidding across the deck completely out of control. At least one case is known where pilot and plane were lost overside while the plane was being taxied into position. A violent roll caused the plane to get out of control and skid along the ice until it went overside.
	-12-

	ASWORG/87 – 13
	1 April 1944.
	2. Number of planes available. This depends on the plane carrying capacity of the CVE, the number that are in mechanical operating condition, and of these, the number that are fueled up, loaded with machine gun bullets and depth charges. It is nearly impossible to satisfy all of the conditions simultaneously. Planes are lost at sea so the total number is diminished as the cruise progresses. It is unusual not to have at least one plane laid up for repair or overhaul. Two or three planes laid up is common and as many as six may be laid up on rarer occasions. Minor deck crashes involving broken wing and elevator tips, bent propellers, broken tail wheels and landing gear are comparatively common. It takes time to make these repairs. In order to place the planes back into service as soon as possible, repair shops operate with full complement 24 hours a day.
	Planes are inspected after each flight by Engineering Inspection Crews. The inspection includes landing gear for cracks and damages, bad tires, leaky oleo struts and damaged tail wheels, the hydraulic system, the arresting hook for operation and correct weight, the engine for oil leaks and loose spark plug leads. The planes have no regular overhaul period on board other than checks every thirty hours. On these checks, both plane and engine are given a thorough inspection for any trouble that has developed and for any item that may cause trouble in the future. All control cables are checked for wear; sheaves, for operation; hydraulic system gone over thoroughly. All operating parts are checked for proper functioning. Oil and spark plugs are changed on TBF’s every sixty hours. F4F’s get oil change every thirty hours and spark plugs change every sixty hours.
	Damaged elevators and rudders lead the list of repairs, with landing gear second. Leaking hydraulic actuating cylinders and timing valves are quite numerous. Repairs of a fairly extensive nature can be made on board ship. Propellers, motors, wheels, wings, elevators and rudders can be replaced. Most repairs on fuselage, landing gear and hydraulic system can also be made.
	Refueling takes place after each landing unless the plane is scheduled for the shop. The refueling is done on the flight deck whenever practicable. Otherwise it is done on the hangar deck. Planes that have had long warm-ups are “topped off” prior to flight. Thus when a plane returns, before it can take off again it must undergo an inspection, be refueled and have her supply of ammunition and depth
	-13-

ASWORG/87 – 14

1 April 1944.

charges replenished. This is a time consuming task so the plane is not immediately available for action after landing.

3. Plane handling and storage. This is one of the greatest and perhaps least appreciated problem of operations aboard the CVE. In a way it is reminiscent of the old Chinese checkers game, where, in order to move a particular piece nearly all the other pieces must be moved first. In the case of the CVE the problem is complicated by introducing another dimension. Planes are shuffled around on both the flight deck and the hangar deck, and the only way from one deck to the other is via two elevators.

        Figures 1 and 2 are scale drawings which indicate the amount of deck storage space available when planes are being landed when the catapult is not in use, and space available when catapulting. If no landings are being made, most of the space aft of the barriers is available for storage during catapult launchings. For deck launchings a row of planes may be stored on the starboard side as far forward as the barriers. A second row can be carried forward as far as the aft elevator.