Interstate TDR-1: the first strike drone to see combat—in the Second World War!

TomLiu126 · March 17, 2025, 5:56pm

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Ground crew on Banika Island preparing a TDR-1 named “Edna III” for an attack on Rabaul. The television guidance equipment in the nose is visible. Other sources claim that the attacks on Rabaul were performed from Green Island. (source: Naval History and Heritage Command)

The Interstate TDR-1 was an unmanned aerial combat vehicle developed by the US Navy during World War II. Being an improved version of the Naval Air Factory TDN-1, it featured the same television and radio command guidance system and the same armament (a torpedo or a 2,000 lb bomb) but had a low-mounted wing and was easier to build. It had space for a cockpit to be piloted in test and ferry flights, and the space was covered with aerodynamic fairings for unmanned operations. Unlike its predecessor, the TDR-1 was tested in action against Japanese cargo ships and land installations, making it the first UCAV to see combat.

History

Our story continues from the TDN-1 and Project Option. While the TDN-1 was successful in testing, it was deemed unsuitable for mass production, so Interstate was asked to produce an improved version, the TDR-1 (some sources instead allege that the TDN-1 and TDR-1 were developed concurrently, and the TDR-1 just happened to be the better one). It shared the same engines, guidance system, and payload options, but had a low-mounted wing instead of a high-mounted one. It was built with a steel frame (supplied by a bicycle company) and covered by moulded wood, hence reducing the usage of strategic materials. It had space for a cockpit to be piloted in test and ferry flights, and the space was covered with aerodynamic fairings for unmanned operations. During unmanned operations, the TDR-1 was controlled by an operator in a modified Grumman TBF/TBM Avenger. The operator could control the drone’s flight using a joystick and could set operational codes for the autopilot using a telephone dial.

By the time the TDR-1 came to maturity, the tide of the war had already turned. The US was on the offensive, and there seemed to be little need for unconventional weapons like these strike drones. After intensive lobbying by leaders of the Special Air Task Force (SATFOR, the new name for Project Option), the Special Air Task Group One (STAG-1) was approved to perform combat trials of the TDR-1 and was deployed to the South Pacific in May 1944. On 30 July, the first attack was performed by four TDR-1s carrying 2,000 lb bombs against a grounded Japanese freighter. Later, STAG-1 was deployed to Stirling Island to perform strikes against Japanese positions on Bougainville Island. STAG-1 also participated in the attacks on Rabaul, probably as part of Operation Cartwheel. While image captions from the Naval History and Heritage Command claim that the attacks were launched from Banika Island, Newcome claims that one squadron (VK-12) of STAG-1 was deployed to Green Island for the attacks (Green Island is much closer to Rabaul than Banika Island, so it does make more sense). The drones flew through heavy anti-aircraft fire to perform their strikes, while the pilots and operators safely orbited 6 to 8 miles away from the action. No crew were lost in STAG-1 operations, proving the effectiveness of drone operations. In some of the later attacks, after dropping their bombs the TDR-1s attacked Japanese cargo ships by ramming them, reminiscent of the Kamikaze attacks performed by the Japanese themselves, albeit without the same sacrifice of human life. In total, 46 attacks were made, of which 21 hit their targets (Newcome claims 50 attacks, with 31 successes). However, the US was very clearly winning the war by then, and the strike drone program was seen as unnecessary and cancelled. Several improved prototypes were produced, but none saw further development. Nevertheless, their work proved influential for the cruise missiles and UCAVs we see today. At the 1990 reunion of STAG-1, the Secretary of the Navy sent a congratulatory letter, stating: “The vision, determination, and dedication with which you performed your secret duties during World War II laid the groundwork for today’s modern cruise missile.”

Specifications

Crew: 0 or 1
Weight: 2700 kg
Engines: 2x Lycoming O-435 piston engines, 220 hp each
Speed: 225 km/h
Weaponry: one torpedo or one 2,000 lb bomb (Newcome also mentions a loadout of "a combination of ten 500- and 100-lb bombs)