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Torpedo Bomber!

Grumman's TBF and Eastern's TBM were America's last torpedo bombers

by Randy Wilson

Copyright 1999 by the Confederate Air Force and Randy Wilson. All rights reserved.

Originally published in The Dispatch magazine, Volume 24, Number 1, Spring, 1999 edition. If you are interested in subscribing to The Dispatch please write to The Commemorative Air Force, ATTN: Dispatch Editor, PO Box 62000, Midland, TX 79711-2000 or call (432) 563-1000. Reproduced with permission.

As the twentieth century dawned, one of the most feared Naval weapons was the self-propelled torpedo, launched from small, fast torpedo boats or submarines. Less than a decade after the Wright brothers’ first powered flight, the airplane was being tested as an aerial torpedo carrier.

On July 28, 1914, the first aerial torpedo was launched from a Royal Navy Short seaplane by Lt. A. M. Longmore. The U. S. Navy first experimented with aerial torpedoes in late 1917, when a 400-pound dummy torpedo was dropped from a seaplane and ricocheted back into the air, almost hitting the plane. Since the aircraft of the day could lift only about 600 pounds of bombs or other ordnance, and the normal shipboard or submarine torpedo weighed 1,500 pounds or more, the torpedo bomber was not yet a reality.

Early U.S. Torpedo Bombers

Shortly after the end of the First World War, the development of reliable aircraft engines of 400 to 600-horsepower and refinements in torpedo designs produced the first operational torpedo bombers. In the U.S., these included the single-engine Douglas DT and the twin-engine T2D float planes. By the late 1920s and early 1930s, the U.S. Navy was equipped with Martin T3M and T4M biplane torpedo bombers capable of operation on floats from the water, or fitted with wheels, from the decks of aircraft carriers. The Great Lakes Company also produced a variant of Martin’s T4M design for the Navy.

The earliest torpedo bombers could only carry a small torpedo, often a shorter, lighter version of the standard 17.7-inch diameter weapon, or an even smaller 14-inch version. Aerial torpedoes had an effective range of less than 2,000 yards and carried an explosive warhead smaller than standard torpedoes. A successful attack required that the torpedo be dropped no farther than 1,000 yards from the target ship.

From Biplanes to Monoplanes

In 1934, the U.S. Navy ordered prototypes of a new torpedo bomber from both Douglas and Great Lakes, the later proposing a biplane design. The Douglas TBD was chosen and became the first production monoplane to enter U.S. carrier service. Delivery of the TBD Devastator began in 1937, and its 900-horsepower Pratt & Whitney R-1830 engine allowed it to carry a 1,000-pound bomb or 2,000-pound torpedo.

In other countries, development of the torpedo bomber followed varying paths. Japan issued specifications for a monoplane design in 1935, which resulted in the efficient Nakajima B5N, later code-named KATE. Germany relied on twin-engine float planes such as the Heinkel He 115 early in the war but also fitted land based He 111 and other medium bombers to carry torpedoes.

In Great Britain, the Royal Navy entered the war with the Fairly Swordfish as its principal torpedo bomber and reconnaissance aircraft. The Swordfish was a large open cockpit biplane and was affectionately called the "Stringbag" due to its wire bracing and seeming ability to carry almost any kind of load into the air. Despite a speed of less than 100 knots when loaded with a torpedo, the Swordfish proved deadly against the Italian fleet in a daring night torpedo attack on the harbor of Taranto on November 11, 1940. The German battleship Bismark was also caught and sunk by the Royal Navy after being damaged and slowed by a torpedo launched from a Swordfish.

Torpedo Development

The standard U.S. aerial torpedo in World War II was the 22.4-inch Bliss-Leavitt Mark XIII. Thirteen feet long, early versions carried 401 pounds of TNT, later increased to 600 pounds of Torpex high explosive. With the larger warhead, the torpedo weighed over 2,200 pounds. The early versions were likely to break up or be damaged if dropped from a height of greater than 50-100 feet at an airspeed faster than 110 knots. Such a low and slow attack proved disastrous to the TBDs in the first U.S. naval battles with Japanese warships. During the Battle of Midway on June 4, 1942, Torpedo Squadron 8 (VT-8) lost every one of its Devastators and all but one of their crew, Ensign George Gay, without seriously damaging the enemy.

Other countries' aerial torpedoes tended to be smaller and lighter than the U.S. Mark XIII, and most could be dropped successfully at a higher altitude and airspeed. The Japanese 17.7-inch Type 91 Mod 3 aerial torpedo used early in the war was 17’ 4" long and weighted 1,872 pounds with a 529-pound warhead. The British Mk XII was similar in size but lighter with an explosive charge of 388 to 433 pounds. Germany’s F5b 17.7-inch aerial torpedo was of Norwegian design, however the Italian Fiume torpedo was also used under the designation F5w. Explosive charges ranged from 397 to 441 pounds.

Birth of the Avenger

In 1940, the U.S. Navy had placed a contract with Grumman for a new torpedo bomber to replace the Douglas TBD. The new design, designated the TBF, was larger and faster than the Devestator, and carried its torpedo or up to 2,000 pounds of bombs or depth charges in an internal bomb bay. Defensive armament included a 0.50-caliber machine gun in a powered turret and a hand-held 0.30-caliber gun mounted in a ventral tunnel. The prototype XTBF-1 first flew on August 1, 1941 but problems with its 1,700-horsepower Wright R-2600 engine and the crash of the prototype kept the first production TBFs from being delivered until early 1942. Directional stability was improved in production TBFs by the addition of a large dorsal fin.

The Grumman TBF acquired the name Avenger shortly after the Japanese attack on Pearl Harbor brought America into the war. The first six Avengers were intended to equip VT-8 on the USS Hornet in time for the Battle of Midway, but the carrier had sailed from Pearl Harbor when the planes arrived. Flown from Hawaii to Midway, the six TBFs launched from Midway to attack the Japanese fleet on June 4, 1942 but only one Avenger returned. While many new designs suffer in their first exposure to combat, the TBFs’ losses in their first battle were primarily due to the limitation of their primary weapon, the Mark XIII torpedo. Fortunately, the TBF was quickly found to be well adapted to many roles beside that of the nearly suicidal torpedo attack.

In early 1942, Grumman’s priority was focused on developing the F6F Hellcat fighter, and the Navy urged the company to turn over production of its other designs, the Wildcat and Avenger, to General Motors. GM had several automobile plants already producing component parts for aircraft, so why not the whole plane? In March of 1942, a contract was signed for 1,200 Avengers to be constructed at GM’s Eastern Aircraft plant in Trenton, New Jersey. The Eastern Avengers were designated TBM-1s but were basically identical to the Grumman TBF-1.

Grumman assembled a few TBFs using Parker-Kalon (PK) sheet metal screws in place of rivets. These"PK" aircraft allowed Eastern workers and engineers to take apart the aircraft and study how every piece was fitted. Differences in building automobiles versus aircraft slowed initial production of TBMs, but by March 1943, Eastern was turning out TBM-1s without any further help from Grumman, which built the last of almost 2,300 TBFs in December of that year.

The three man crew of the Avenger consisted of a pilot, gunner/radio operator and bombardier/radar operator, as even early TBF-1s were often fitted with air to surface Type B (ASB) radar. When not carrying a torpedo, the Avenger could haul four 500-pound bombs or depth charges in its bomb bay. Forward firing armament in the original design was a single 0.30-caliber gun mounted in the engine cowling, but this was changed to two wing-mounted 0.50-caliber guns in the TBF/TBM-1C models which entered service in late 1943.

Less Weight and More Power

As more equipment and weight was added to the Avengers, their performance began to suffer. In early 1943, the Navy wanted Eastern to find ways to lighten the Avenger and give it more power, as its use from smaller escort carriers in the anti-submarine role was becoming more important than torpedo attack. The first result was the TBM-3, with 1,900-horsepower from its uprated Wright R-2600-20 engine. The new version began to roll off the assembly line at the Trenton plant in April of 1944. In December of that year, modifications to further reduce the aircraft’s weight by over 300 pounds resulted in the TBM-3E, which became the last major version of the Avenger to be produced.

Although Avengers participated in torpedo attacks on Japanese capital ships during the latter half of the war, the poor reliability of the Mark XIII aerial torpedo resulted in relatively few hits. Most ships attacked were finally sunk by dive bombing or Naval gunfire. By 1944, TBMs were most often employed in glide bombing, strafing and rocket attacks against enemy shipping and land targets, or teamed with Eastern-built FM-2 Wildcats to form anti-submarine hunter-killer teams. Four 3.5 or 5-inch air to surface rockets carried under each wing gave the Avenger a broadside equal to a destroyer against surface targets.

British Tarpons

Grumman built 402 TBF-1Bs for Britain’s Fleet Air Arm under the Lend-Lease Program in 1942, where they were initially called Tarpons. The name was changed to Avenger in early 1944 to avoid confusion when operating with American carrier groups in the Pacific. Almost a thousand Tarpons/Avengers entered British service, including 222 TBM-3s, and some Avengers were flown by the Royal New Zealand Air Force. British Avengers also served in the Atlantic in the anti-submarine and anti-shipping roles and attacked targets on the European coast, including German V-1 flying bomb launching sites. The last Avenger squadrons in Fleet Air Arm service were disbanded less than a year after the end of the war.

Postwar Service

With the end of the Second World War, the traditional torpedo bomber had become obsolete, however, other uses were found for the Avengers. The TBM-3R was modified to carry seven passengers by removing the gun turret, allowing it to transport personnel and equipment to and from carriers in what became known as "carrier-onboard-delivery" or COD. A small number of TBM-3N built at the end of the war also lost their turrets to make room for larger radar installations for night attacks, and helped develop night and all-weather attack methods into the 1950s.

The TBM-3S was a specialized anti-submarine warfare (ASW) version, again without a turret, while the TBM-3Q and TBM-3W were airborne early warning versions. The TBM-3U was a utility "hack" used for various duties including target towing. All or most of these postwar variants were converted from TBM-3 airframes, and some carried only a two-man crew. Many lost their arresting hook as well as their turret.

By the time the Korean War erupted in 1950, only a few TBM-3Rs transports and TBM-3U utility versions were still in U.S. service. However, Avengers continued to serve in the ASW role with other nations, including Canada, France, the Netherlands and New Zealand until 1960. The Japanese Self Defense forces retired their last TBM in 1962.

Even after their retirement from military service, Avengers continued to do aerial battle with forest fires and agricultural pests into the 1980s. Their cavernous fuselage and good weight lifting ability kept them busy in these roles until the cost of spare parts and engine overhauls made them uneconomic. Those that survived such difficult civilian service are today enjoying a more gentle life. Many, including the Ghost Squadron’s Avenger, are flown and displayed at air shows, where they remind younger generations of the courage and sacrifices of torpedo bomber crews more than fifty years ago.

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