Hawaii detected the Japanese attack formation at a range of 132 miles (212 km), but this crucial plot was misinterpreted due to a grossly inefficient reporting chain. One other metric radar was developed by the SCL. After Pearl Harbor, there were concerns that a similar attack might destroy vital locks on the Panama Canal. A transmitter tube that delivered 240-kW pulsed power at 600 MHz (0.5 M) had been developed by Zahl. A team under John W. Marchetti incorporated this in an SCR-268 suitable for picket ships operating up to 100 miles offshore. The equipment was modified to become the AN/TPS-3, a light-weight, portable, early-warning radar used at beachheads and captured airfields in the South Pacific. About 900 were produced. A British ASV Mk II sample was provided by the Tizard Mission. This became the basis for ASE, for use on patrol aircraft such as the Consolidated PBY Catalina. This was America's first airborne radar to see action; about 7,000 were built. The NRL were working on a 515-MHz (58.3-cm) air-to-surface radar for the Grumman TBF Avenger, a new torpedo bomber. Components of the ASE were incorporated, and it went into production as the ASB when the U.S. entered the war. This set was adopted by the newly formed Army Air Forces as the SCR-521. The last of the non-magnetron radars, over 26,000 were built. A final "gift" of the Tizard Mission was the Variable Time (VT) Fuze. Alan Butement had conceived the idea for a proximity fuse while he was developing the Coastal Defence system in Great Britain during 1939, and his concept was part of the Tizard Mission. The National Defense Research Committee (NDRC), asked Merle Tuve of the Carnegie Institution of Washington to take the lead in realising the concept, that could increase the probability of kill for shells. From this, the variable-time fuze emerged as an improvement for the fixed-time fuze. The device sensed when the shell neared the target – thus, the name variable-time was applied. A VT fuze, screwed onto the head of a shell, radiated a CW signal in the 180–220 MHz range. As the shell neared its target, this was reflected at a Doppler shifted frequency by the target and beat with the original signal, the amplitude of which triggered detonation. The device demanded radical miniaturisation of components, and 112 companies and institutions were ultimately involved. In 1942, the project was transferred