A great print of a watercolor by James Gardner, “A British Anti-Aircraft Battery in Action,” likely either during or just after the Battle of Britain.
The weapons seem to be Ordnance QF 3.7-inch Heavy AA Gun used in conjunction with spotlights, spitting sheets of flame into the night sky at unseen intruders overhead. The QF 3.7 was the most common British heavy AAA mount of the war, considered roughly equivalent to the German Flak 88, and was judged quite effective.
Here’s what it looked like in real life.
In some equally beautiful images, try on these original Kodachromes of QF 3.7s, courtesy of the Library and Archives of Canada.
Incidentally, Garnder, the painter behind the top image, was Chief Deception Officer (what a great title!) at the RAF Camouflage Training School during the war and lived until 1995.