Class AM1 was allocated to the prototype AC electric multiple units, converted from fourth-rail DC electric stock in 1952 and used on the Lancaster/Morecambe/Heysham route. This route had been electrified by the Midland Railway at 6.6 kV, 25 Hz AC, but the frequency was changed to 50 Hz in 1953 to test the prototype AM1 stock. The line was closed to passengers and the stock withdrawn in early 1966. Unlike classes AM2-AM11, which became TOPS Classes 302-311, class AM1 was withdrawn before it could take its place in the system as class 301. However, it was the success of these tests that contributed to the decision to choose 25 kV AC overhead electrification as standard in Great Britain outside the Southern Region.
The electric service started on 17 August 1953, and the trains, very much seen as experimental, ran until 16 April 1966, when they were withdrawn. Each of the four electric trains contained different unique features to test them, and although the original MR electrification equipment, which was still in situ, was used in places, other sections were used for trials of the proposed BR standard electrification features. There was little demand for the service outside the summer holiday season, and the presence of the duplicate former-LNWR route between the Lancaster and Morecambe allowed a replacing diesel service to use that route. The service was complex to operate, for from the main line ex-LNWR Lancaster Castle station it ran downhill a short distance to the ex-MR Lancaster Green Ayre station, where trains reversed to run westward along the River Lune to Morecambe Promenade station, where trains reversed again to run to Heysham.