55th (Kent) Heavy Anti-Aircraft Regiment, Royal Artillery was a volunteer air defence unit of Britain's Territorial Army from 1925 until 1955.

In World War II it defended the Thames Estuary, Medway Towns and Dover during The Blitz and later served in Iraq and North Africa.

For a number of years the regiment consisted of this single battery (which was redesignated 163 (Kent) Bty in April 1936) and in turn formed the only unit of 28th Air Defence Brigade.

[11] Opportunities for action were rare during the Phoney War, but on the night of 22/23 November 1939 the HAA guns of 28 AA Bde ('Thames South') combined with those on the other bank of the river ('Thames North') to engage at least two enemy mine-laying aircraft that had strayed into the mouth of the Estuary.

On 18 August, for example, German air raids appeared over RAF airfields at West Malling, Manston, Kenley, Biggin Hill, Gravesend and the town of Sevenoaks, all within four and a half hours in the afternoon.

On 7 September heavy raids up the estuary attacked oil wharves at Thameshaven, Tilbury Docks and Woolwich Arsenal: a total of 25 aircraft were destroyed by AA guns and fighters.

[15][16] After 15 September the intensity of Luftwaffe day raids declined rapidly, and it began a prolonged night bombing campaign over London and industrial towns (The Blitz).

The lightweight No 3 Mark III ('Baby Maggie') mobile gunlaying radar sets proved too fragile for landing over an open beach.

Also, radio and telephone communications could not be established, and Allied airborne formations overflying the beachheads to their drop zones suffered badly from friendly fire.

[28][29] During the invasion of mainland Italy in late 1943, beginning the Italian Campaign, 55 HAA Rgt at first remained in Sicily defending Augusta.

After the breakout from Anzio in May 1944, 66 AA Bde took over that area, and then followed Fifth Army up the west coast through Rome until it reached Livorno, where 55 HAA Rgt defended the important supply port.

[33] The Luftwaffe 's strength in Italy growing weaker, AA defence became less important and Eighth Army's HAA guns were increasingly used in the medium artillery role to support the ground troops.

The effectiveness and accuracy of the 3.7-inch gun and the ample supply of AA ammunition made HAA units a useful addition for the artillery commanders.

55 HAA Regiment spent months of the Italian campaign engaged in this way as corps medium artillery, often working with Air OP spotters.

12 Bde's remaining units were spread thinly to defend a large number of roads, ports and railheads for Eighth Army and landing grounds for the Desert Air Force.