SCR-270 radar

The SCR-270 was developed by the Signal Corps Laboratories at Fort Monmouth, New Jersey, under the direction of Colonel William Blair and engineer Roger B. Colton. It was the first mobile long-range radar in the U.S. Army inventory, designed to be transported on trucks and set up in under an hour. The system used a 100 MHz carrier wave with a pulse width of 10 microseconds and a pulse repetition frequency of 621 Hz, achieving a peak power of about 200 kW. The antenna was a 12-element array mounted on a rotating platform, providing a beam width of about 12 degrees. The radar could detect large aircraft at ranges up to 120 miles and was later improved with the SCR-271, a fixed-station variant.

The SCR-270 saw its most famous action on December 7, 1941, when a mobile unit at Opana Point, Oahu, detected a large formation of aircraft approaching from the north at 132 miles. The operators, Privates Joseph Lockard and George Elliott, reported the contact to the Information Center, but the officer on duty, Lieutenant Kermit Tyler, assumed it was a flight of B-17s arriving from the mainland and told them not to worry. The radar plot was later recognized as the incoming Japanese attack force. The SCR-270 was also used in the Pacific and European theaters for early warning and ground-controlled interception, though it was gradually replaced by more advanced microwave radars by 1944.

The SCR-270 consisted of several components: the transmitter (BC-720), receiver (BC-740), and a 30-foot trailer-mounted antenna. The system required a crew of about 10 men and could be erected in 30 minutes. The radar operated in the HF band, which limited range resolution but allowed detection of aircraft at long distances. A fixed-station version, the SCR-271, was installed at various coastal sites in the U.S. and Panama. The SCR-270 was also used for experimental purposes, including the first U.S. radar detection of a ship at sea in 1939. Later, a modified version, the SCR-270-B, incorporated improvements in receiver sensitivity and antenna stabilization.

Beyond Pearl Harbor, the SCR-270 played a role in the development of radar countermeasures. In 1942, the Japanese captured an SCR-270 in the Philippines, which may have influenced their radar development. The radar was also used in the U.S. to test the concept of radar-absorbing materials, with early experiments using carbon-loaded rubber. The SCR-270's design influenced the British Chain Home system, though the two were developed independently. After the war, many SCR-270s were sold as surplus, and some were used for weather observation and even for tracking early satellites in the 1950s. The radar is also notable for its use of a single antenna for both transmission and reception, a design that was advanced for its time.

Early-warning radar

A radar system designed to detect incoming aircraft or missiles at long range, providing advance warning.

HF band

High-frequency radio band, typically 3 to 30 MHz, though the SCR-270 operated at 100 MHz.

Pulse repetition frequency

The number of pulses transmitted per second in a radar system.