By Tommy H. Thomason

Saturday, July 18, 2015

Post-War Eastern TBM Variants

25 July 2015: Added  background information on the TBM-3P
19 July 2015: Updated with additions, corrections, and other changes.

Rick Morgan (http://rickmorganbooks.com/index.html) and I have continued to explore the poorly documented post-war history of the various variants of the Eastern Aircraft TBM-3. The Navy still had lots of them after the war. Since they were big and easily modified, they were readily adaptable to other missions besides torpedo, glide, and level bombing that were their raison d'etre.

Most were modified from TBM-3Es. In most cases, the addition of the E would simply mean the addition of electronic equipment, in this case provisions for carrying the APS-4 radar on a stores pylon under the right wing. However, the designation is also associated, possibly coincidentally, with a redesign by Eastern to reduce weight by about four hundred pounds. One of those changes was probably the location of the tailhook, which had been internally housed on all TBFs and prior TBM production.  Most TBM-3Es delivered from Eastern probably had the external tailhook. This is an example.


There is evidence that the weight reduction effectivity in production (like the tailhook change, deletion of tunnel gun provisions and some armor, etc.) was not the same as for the APS-4 provisions. As a result, the first production -3Es did not have the external tailhook. It is also possible, even likely, that TBM-3s were subsequently modified to the E configuration (i.e. APS-4 provisions) at Navy repair and overhaul facilities but retained the internal tailhook.

Based on the information provided on Joe Baugher's invaluable listing of Bureau Numbers (see http://www.joebaugher.com/navy_serials/navyserials.html) and elsewhere, it appears that one TBM-3E production lot used a block of Bureau Numbers from a cancelled BuAer contract:

Bureau Numbers                 Mfg Number                Model

22857-23656                       1-800                            TBM-3

68062-69538                       801-2277                      TBM-3

85459-86292                       2278-3111 (834)           TBM-3E

53050-53949                       3112-4011 (900)           TBM-3E

91107-91752                       4012-4657 (646)           TBM-3E

These out-of-sequence BuNos explain why many "older" TBM-3Es, i.e. with 53XXX BuNos, are configured with an external tailhook even though its effectivity reportedly occurred at either BuNo 85566 or 86175. It also explains erroneous statements to the effect that most TBM-3Es did not have the external tailhook when in fact most do.

For sure there are TBM-3Es with the APS-4 radar and an internal tailhook. In his comment below, Pablo Montero provided a link to this example, which is reportedly a VMTB-234 Avenger circa 1945. It looks like there is an E at the end of the type designation on the vertical fin but as is frequently the case, the BuNo cannot be read.

The next interesting issue is the alphabet soup of TBM-3 variants. A suffix was used when a change was "major" and intended to be permanent, with occasional exceptions (see TBM-3J below). Some are well known:

TBM-3D: A late-war modification to add an APS-3 radar hard mounted on the right wing and ECM (Electronic Counter Measure) equipment. The gun and associated hardware was removed from the turret and the lower compartment by VT(N)-90  to reduce weight since its primary mission was night attack.
TBM-3W: A late-war modification to add an APS-20 radar in a large belly-mounted radome for airborne early warning. Some were converted from TBM-3s like 89471 so it had an internal tailhook.

Some were converted from TBM-3Es like 53894 so it had an external tailhook.

TBM-3R: A Korean War-era modification for COD (Carrier On-board Delivery); see http://tailhooktopics.blogspot.com/2013/01/tbm-3r-cod.html

TBM-3S: A post-war modification to remove the defensive armament and add ASW mission equipment. It was teamed with a TBM-3W variant to provide submarine hunter-killer capability as a placeholder for the AF Guardian. There were variations in the mission equipment and the canopy modification (one was designated TBM-3S2 to distinguish it from the 3S). Note that a crewman now occupies the compartment aft of the pilot.

TBM-3U: A TBM-3 modified to tow targets and for general utility use.
Note that BuNo 69400 was probably delivered from Eastern as a -3 and subsequently modified to carry an APS-4 radar pod under the right wing.

Less well known and sometimes misidentified are the TBM-3N (see http://thanlont.blogspot.com/2015/07/tbm-3n-versus-tbm-3q.html) and TBM-3Q (see http://rickmorganbooks.com/tbm-3q-avenger.html). For example, as Rick points out in his excellent post on the latter, it did not have a belly-mounted radome like the TBM-3W as usually stated in TBM books and online summaries.

And then there are the TBM variants for which we have yet to find documentation, much less photographs. Through the magic of copy and paste, these are identified on many web sites as follows:

TBM-3H: TBM-3 modified for surface search radar

TBM-3J: TBM-3 equipped for all-weather operations (i.e., with wing and tail surface deicing)

TBM-3L: TBM-3 equipped with a retractable searchlight in bomb bay

TBM-3M: TBM-3 conversion as missile launcher

TBM-3P: TBM-3 conversion for photo-reconnaissance

Of these five, for sure the TBM-3P and TBM-3L are correctly identified per Navy documentation dated November 1944.

The TBM-3P was a TBM-3 "equipped with a trimetregon (sic) camera". Rick Morgan has found "less than 10" in CASU (Carrier Aircraft Service Units) pools in San Diego and Pearl Harbor in the 1946 Allowance Lists (some are listed as TBM-3EP, which suggests that "TBM-3Ps" were converted from TBM-3s). CASUs were repair and maintenance centers at some naval air stations; they were also a storage point for airplanes that could be issued to squadrons to replace attrition. The trimetrogon camera installation actually utilized three cameras, left and right oblique and vertical, taking pictures simultaneously. This is the installation in a B-17 (see https://historicairphotos.wordpress.com/2014/05/21/trimetrogon-photography/)
The pictures overlapped so they provided complete coverage from side to side.
The TBM-3P camera installation was probably located in the lower (radioman's) compartment. Since mapping, as opposed to strike-damage assessment, was not a primary air-group mission, the TBM-3P was probably little utilized and appears to have had a short career. No pictures of one have been identified as such.

The same document lists the TBM-3L as a "TBM-3, 3D, or 3E equipped with a searchlight mounted in the bomb bay". Note that the TBM-3D had provisions for a searchlight mounted on a pylon under the left stub wing but since this was "detachable", the suffix L did not apply. (In any event, utilizing the bomb bay for this purpose seems counterproductive, which may be why there aren't too many pictures of the type—I have yet to see one.)

The description of each of the other three TBM variants is dubious. A Navy History and Heritage Command document (HERE) does not list the H and the M and identifies the J as a "utility plane".

At the time, the suffix H was used to designate an airplane modified to be a "hospital", i.e. to transport wounded personnel. That's a possibility, although no TBM-3Hs have been identified. There was reportedly a modification of the TBM-3W's radar to optimize it for submarine-snorkel detection but this would have, if anything, probably resulted in a modification to the existing designation (there is a TBM-3W2, for example).

There may have been TBMs with deice boots but they were not designated TBM-3Js. These were TBMs modified with provisions for target towing, the forerunner of the TBM-3U. However, they retained the carrier-basing and ordnance capability; as a result, the designation of a TBM with this capability depended on whether the tow equipment was installed or not! See the June 1947 issue of Naval Aviation News. The TBM-3U had a permanently installed tow reel and all offensive and defensive mission equipment removed.

The TBM-3M, if there were any, was more likely a modification for weather reconnaissance like the PB4Y-2M, which was the purpose of the suffix at the time. None have been identified.

On the other hand, there are a couple of TBM modifications that we have pictures of but little or no additional information. The first is something in the bomb bay of  TBM-3E BuNo 91704 in a picture provided by Jim Hawkins via Steve Ginter. It looks like there is an opening at the bottom of the aft end of the pod and what might be static discharge wicks or antennas on the bottom of the pod. It could be an early ECM pod installed on this TBM for inflight testing.

Another is a TBM marked as a -3E, reportedly BuNo 69465 at Pax River on 18 January 1946, provided by Jim Sullivan (the TT on the cowling indicates that it was assigned to the Tactical Test division at the time). It was reportedly an attempt by Eastern to compete with the new single-seat BT—soon to be changed to A for attack—airplanes from Douglas, Martin, et al.


Saturday, July 11, 2015

TBM-3N versus the TBM-3Q

I was recently asked if I had any pictures of a TBM-3Q. First, I had to refresh my memory of the type, one of several modifications of TBM-3Es, a veritable alphabet soup of repurposed Turkeys.

The TBM-3E was the last production model, redesigned in detail to reduce weight and add provisions for an APS-4 radar pod under the starboard wing.  The Eastern Aircraft Division of General Motors built 1,480 as the war was winding down and Navy contractors were completing the development of various single-engine attack airplanes like the AD Skyraider that would replace it and the Curtiss SB2C. The most obvious external difference was that the tailhook was stowed under the aft fuselage rather than within it.

The TBM-3Q was one of the first carrier-based airplanes configured specifically for electronic reconnaissance although it retained its ordnance-delivery capability so ELINT (short for electronic intelligence) was more of a collateral duty. It could also be used to "home-in" on enemy ships and shore-based defenses that utilized radar and jam the capability.

I found this picture of two "TBM-3Ns" on the excellent web site of the National Naval Aviation Museum (http://www.navalaviationmuseum.org/).

I thought that they were actually TBM-3Qs because they did not have turrets (according to one online description of the TBM-3Q, a characteristic of this conversion) and had ECM (Electronic Counter Measure) antennas identical to those on the Martin AM-1Q and the various Douglas Skyraider Qs.
I so informed the museum's library staff and got the immediate and polite response that to the best of their knowledge, the Ns did not have a turret and the Qs did. Another strike against online research.

The TBM-3N Radar Operator's position:

It appears that the TBM-3N was a postwar -3E modification to perform night and all-weather attack missions with updated electronic countermeasure avionics as a placeholder for the forthcoming Skyraider. Rick Morgan looked at some postwar location lists and estimates that no more than 30 conversions were accomplished. He found that some were assigned to the air groups linked with FDR (CVB-42) and Saipan (CVL-48) in early 1947 and early 1947/8 respectively. However most were operated by the night composite squadrons that provided detachments to deploying air groups, first VCN-1 and -2 and then their successors, VC-3 and -4. (For a brief summary of the role of composite squadrons, see http://thanlont.blogspot.com/2013/12/composite-squadrons-and-detachments.html.) TBM-3Ns were also operated by the two Fleet All-Weather Training Units, the Pacific (the two pictured above, circa 1950) and Atlantic

This is a picture from the files of the National Naval Aviation Museum of a VCN-2 TBM-3N landing on Philippine Sea in 1948.
 Note the lack of a turret.

There was wartime precedence for the removal of the turret for night attack (and in fact, none of the Navy candidates for its postwar carrier-based attack requirements, day or night, had defensive armament). VT-90N removed the turret hardware (but not the enclosure) from its TBM-3D's in late 1944 or early 1945 to lighten them. If you look closely at the turret, you'll see that a crewman is sitting there, sans machine gun.
Note that the -3D was optimized for night attack with an APS-6 radar hard-mounted to the wing and various ECM antennas. Why was it not a -3N? Good question. For my attempt to unravel the World War II Navy airplane designation suffix history, see http://thanlont.blogspot.com/2014/03/navy-aircraft-designation-suffixes-redux.html and the links therein.

So what did the TBM-3Q look like? Larry Webster came up with this picture of one in an old Japanese aviation enthusiasts' magazine.
It has the aft-fuselage antennas like those on the TBM-3N but also retains the turret.

Rick Morgan was also exploring this question as well. His TBM-3Q post that resulted is far more detailed than the one I was coming up with. See http://rickmorganbooks.com/tbm-3q-avenger.html.

Your guess is as good as mine as to why the turret was retained on the -3Q. Mine is that there was a risk that the focus of its intention to collect electronic information for future strike-mission planning might take umbrage at the fact. As it turned out, several unarmed land-based "spy" planes were shot down during ELINT missions. For incidents involving the U.S. Navy, see https://www.nsa.gov/about/_files/cryptologic_heritage/publications/coldwar/dangerous_business.pdf

Rick Morgan opined that they retained the turrets because they were assigned to VT/VA squadrons that were primarily equipped with TBM-3Es that retained the turret. Since they could be assigned to day strikes along with the other Avengers in the squadron, their crews wouldn't want to be be defenseless in that event, much less likely to be singled out initially because of the lack of a turret.

Friday, July 3, 2015

Call Sign Boron?


A couple of people have asked me about the picture of the VA-55 A-4C above. It was reportedly taken at Danang circa 1967 when the squadron was deployed with Constellation.

Although guesses included a call sign, it was a composite-structure test specimen, installed on a fleet aircraft for a evaluation in operational usage.

From the AIAA paper by A.V. Hawley and M. Ashizawa presented in October 1968 (see HERE for a link to the PDF, which was found by Phil Friddell):

"The (A-4) flap was initially selected as a suitable component for obtaining flight experience with boron filaments. The existing production aluminum flap was redesigned utilizing boron skins supported by a full-depth honeycomb core, while retaining some of the basic component aluminum parts for interchangeability reasons. A second flap design, utilizing graphite as the composite reinforcement and developed in accordance with advanced structural element concepts such as molded graphite parts to replace aluminum rib and hinge fittings was developed. The choice of skin layup and core geometry is explained. It is shown to depend not only on the strength and stability of the skin but also on the temperature and pressure conditions that exist during the cure and secondary bonding. Emphasis is placed on the problems encountered during the design and development phases rather than on those which came to light during the final detailed analysis."

The test specimen was prominently identified, in part because of the health hazards presented by boron fibers when they are burned, and since it was non-standard from a repair standpoint. "Boron" was also a reminder that the component, even damaged, was of interest to the Bureau of Aeronautics and its creators.

Aircraft structure incorporating boron composites were subsequently used in the F-14 among other aircraft.