Navy Assault Drones (1936-1944)

The last surviving TDR-1 assault drone at the Naval Aviation Museum in Pensacola, FL.

The United States Navy has always had a rather mixed history with antiship missiles. While its failure to widely field such weapons except for a brief period at the end of the Cold War has given it a reputation for being backwards in the area, in fact it was the very first to begin serious work on them. Although overshadowed in history by the German HS-293 and Fritz-X glide bombs, the United States actually fielded far more advanced weapons during the war in the form of the ASM-N-2 Bat and TDR Assault Drone. It is the latter of these two missiles that will be the subject of this post.

The genesis of the assault drone program came in July 1936, when the Navy began research into a remote controlled aerial target for more realistic antiaircraft gunnery practice (at this point it was limited to towed targets that could not simulate torpedo or dive bombing attacks). This program (later named Project Dog) proceeded rapidly, modifying a number of JH-1 and N2C-2 aircraft for remote control and conducting its first flight on 15 November 1937. These target drones lacked any sort of stabilization or guidance, and were flown by a pilot located in the backseat of a TG-2 chase plane. On 24 August 1938, a JH-1 drone was first used as a target for the aircraft carrier Ranger (CV-4) and on 14 September 1938, an N2C-2 drone first demonstrated the 45º dive bombing profile against the target ship Utah (AG-16).

The JH-1, the first aircraft to fly under remote control during Project Dog

The creation of radio controlled target drones proved to be a serious wakeup call for the Navy, highlighting deficiencies in antiaircraft defenses and paving the way for the peerless systems that proved so valuable during World War II. However, the program manager, Captain Delmar S. Fahrney, saw the potential for these drones to be used as weapons in their own right and in April 1939, he began working on this concept under the program name Project Fox. In March 1940,
the Bureau of Aeronautics officially approved the development of the assault drone. Rather than a missile, this was envisioned as an unmanned torpedo bomber that relied on a radar altimeter and guidance from the drone pilot in the control plane to conduct a low altitude torpedo drop. Project Fox also investigated placing a TV camera in the drone that would transmit the image back to a monitor in the control plane, allowing better accuracy. By February 1941, the TV guidance system had been successfully tested and became a key component of the program.

The N2C-2, the second airframe of Project Dog

Testing of the assault drone began on 9 April 1942, when a TG-2 drone conducted a successful torpedo drop on the maneuvering destroyer Aaron Ward (DD-483). The TV guidance detected the destroyer at a range of 8 miles (while the control plane was 20 miles from the target) and the drone then flew to a torpedo release point just 300 yards from the ship. On 19 April 1942, a simpler attack profile was tested when a BG-1 drone dove into into a target sled that was being towed at a speed of 8 knots. This time the smaller target was detected at a range of 4 miles, but the control plane maintained an impressive 30 mile standoff at the time of impact.

The TG-2, used as both a torpedo drone and as a control plane during Projects Dog and Fox

In May 1942, Admiral Ernest King was shown footage of these tests and ordered the creation of 18 assault drones squadrons with 1000 drones under the program name Project Option. Rather than the converted manned aircraft used in the tests so far, these would be purpose built assault drones produced by Interstate under the designation TDR-1 (the Navy Aircraft Factory also built a variant known as the TDN-1). The TDR was powered by two radial engines, weighed 5900#, and had a wingspan of 48 feet, making it the size of a manned airplane (indeed, it was optionally manned with a detachable cockpit for ferry flights). As with the manned TBM Avenger, the TDR could carry a single torpedo or a 2000# bomb out to 425 miles (although for the TDR it would be a one-way trip). However, it was designed to be cheap and use non-strategic resources, leading to poor performance and a top speed of just 125 knots compared to the 220 knots of the TBM.

A TDR-1 being armed during operational testing, note the nose panel has been removed to reveal the TV camera

But such a massive program ran into opposition from the Bureau of Aeronautics, which objected to diverting resources away from desperately needed manned aircraft to an entirely unproven weapon system.  Thus, in August 1942, the assault drone order was cut in half to 500 aircraft. But with Admiral King's support, the program grew to 2000 drones in March 1943 (although King had actually desired 3000). Testing of the TDR and TDN began in early 1943 and even include operations off the training carrier Sable (IX-81) in August 1943. The control planes for the new assault drones were modified Avenger torpedo bombers designated TBM-1C.

The TBM-1C control plane, note the large belly antenna for drone control

Despite successful testing and support in the highest levels of the Navy, the Bureau of Aeronautics continued to stall, claiming that the mobile nature of the fighting meant that no time could be found for operationally testing this new weapon and that manned aircraft were sufficient anyways. Thus, the program was reduced to 388 drones. Eventually, on 5 June 1944, a TDR unit known as STAG-1 reached the Russel Islands for operational testing, finally conducting an evaluation mission against a beached Japanese freighter on 30 July 1944. Four drones armed with 2000# bombs and shepherded by a pair of TBM-1C control planes scored two direct hits on the freighter. The entire historic mission was captured on film and makes for interesting viewing.

Ultimately the Bureau of Aeronautics convinced Admiral King that the assault drone was not needed and on 8 September 1944, the entire program was ended after only 309 drones had been built (189 TDR, 114 TDN, 2 XTD2R, and 4 XTD3R). However, the story was not quite over yet as STAG-1 managed to secure a 30 day extension of its combat deployment. From September 27 to October 26, another 46 drones were expended against a variety of Japanese targets in the Philippines, scoring 18-29 hits (accounts vary).

What could have been achieved had this revolutionary program been allowed to continue is impossible to guess. With an advanced guidance system that had demonstrated 49-63% accuracy in combat, Project Option easily have led to an extremely capable missile. However, the TDR and TDN airframes with their optional cockpits and separate bombs and torpedoes were a developmental dead-end. Still, if the assault drones had been used more widely the Navy may have realized their potential of and invested in their development. At the very least, greater use of the TDR could well have saved the lives of American pilots assigned to attack well defended targets during World War II and Korean War.