Rodger, 'four by two' also relates to the piece of cloth used to clean rifles with.
As part of Operation Diver (countering V1s) AAA (anti-aircraft guns) guns were redeployed. With the advent from Red-Lab of the radar-based automatic gunlaying, and the proximity fuse, the kill rate by anti-aircraft guns on Buzzbombs rose to ±75%.
Here’s a quote from
Wikipedia, as to the measures taken against the V1 in the ‘special defence zone’.
“The Tempest wing was built up to over 100 aircraft by September; Griffon-engined Spitfire XIVs and Mustangs were polished and tuned to make them almost fast enough, and during the short summer nights the Tempests shared defensive duty with Mosquitoes. Specially modified P-47 Thunderbolts (P-47Ms) with half their fuel tanks, half their 0.5 in (12.7 mm) machine guns, all external fittings and all their armor plate removed were also pressed into service against the V-1 menace. (There was no need for radar—at night the V-1's engine could be seen from 16 km (10 mile) or more away.)”
ALSO
“A deception concerning the V-1 was played on the Germans using double agents. M.I.5 arranged for these agents to provide Germany with damage reports for the June 1944 V-1 attacks which implied that on average the bombs were travelling too far, while not contradicting the evidence presumed to be available to German planners from photographic reconnaissance of London. In fact the bombs had been seeded with radio-transmitting samples to confirm their range, but the results from these samples were ignored in favour of the false eye-witness accounts, and many lives may have been saved by the resulting tendency of future V-1 bombs to fall short of built up areas.”