155th (Mixed) Heavy Anti-Aircraft Regiment was an air defence unit of Britain's Royal Artillery formed during World War II.

After defending the West of Scotland and later London, the regiment was heavily engaged in Operation Diver against V-1 flying bombs, and later was deployed to Antwerp to carry out anti-Diver duties there in the closing stages of the war.

In April its commander-in-chief, Lieutenant-General Sir Frederick 'Tim' Pile, proposed to overcome this by utilising the women of the Auxiliary Territorial Service (ATS).

The ATS was by law a non-combatant service, but it was decided that Defence Regulations permitted the employment of women in anti-aircraft (AA) roles other than actually firing the guns.

[14][15] The Luftwaffe began a new bombing campaign against London in early 1944 (the Baby Blitz), when the city was subjected to 14 raids between 21 January and 18 April.

Defences had been planned against this new form of attack (Operation Diver), but the missiles' small size, high speed and awkward height presented a severe problem for AA guns and the initial results were disappointing.

The guns were constantly in action, but success rates against the 'Divers' steadily improved, until over 50 per cent of incoming missiles were destroyed by gunfire or fighter aircraft.

1 AA Group had to redeploy facing East to form a 'Diver Box' to intercept V-1s launched by the Luftwaffe from aircraft over the North Sea.

[5][23] The regiment arrived at Antwerp in January 1945, taking over Mk IIC 3.7-inch guns on Pile platforms in bitter weather with inadequate hutting, and were immediately in action against the onslaught of V-1s.

The Antwerp 'X' defences under 80 AA Bde involved an outer line of Wireless Observer Units sited 40 miles (64 km) to 50 miles (80 km) in front of the guns to give 8 minutes' warning, then Local Warning (LW) stations positioned half way, equipped with radar to begin plotting individual missiles.

Finally there was an inner belt of Observation Posts (OPs), about 20,000 yards (18,000 m) in front of the guns to give visual confirmation that the tracked target was a missile.