The Ordnance QF 13 pounder Mk III anti-aircraft gun, also known as 13 pounder 6 cwt, was an early British improvisation in World War I to adapt the QF 13-pounder field gun to anti-aircraft use.

[i] This was a standard QF 13 pounder field gun barrel and breech with the addition of a retaining catch to the breech to retain the round when loading at high angles.

[3] Hence the appearance was of a gun barrel with 2 slightly shorter tubes of similar diameter above it.

[3] On the Mk II mount the gun has the appearance of a standard 13 pounder.

The gun's performance was "ballistically poor" and it was only marginally effective against aircraft.