Emmanuel Gustin wrote:

There was a 'Preston-Green' ventral gun mount for a .50 in gun,
which was widespread until the installation of H2S radar
required its removal. Many units improvised other ventral gun
mounts. A simple clear-vision panel, with or without gun, was
a much better solution than the available turrets.

I am reading R. Wallace Clarke's book "British Aircraft Armamant", and
he says that the Preston Green under defence mounting was fitted to all
Halifax Mk III's. Aircraft production was outstripping radar set
production, so it was gun or nothing, not gun or H2S. When H2S
production ramped up, the turrets were replaced by radar scanners.


Some Halifaxes and Lancasters had ventral turrets, but the
Boulton Paul 'R' and the Frazer-Nash FN.64 were of the
retractable periscope-sighted kind and therefore rather useless
even by day. (Coastal Command nevertheless had the FN.64
turret installed on its Halifaxes.)

Can you say what your source is for this, please? According to Clarke,
HP aircraft never seem to have had FN turrets (save for the Harrow).
Coastal Command made use of the FN77 Leigh Light, a modified FN25 under
turret, in its Wellingtons.

The 'low-drag' FN.21A
apparently fitted to some early Manchesters and Lancasters
was a retractable dustbin turret with extending 'shoes' to
accomodate the feet and legs of the gunner, which must have
resulted in a truly enormous amount of drag when lowered.


According to Clarke, the FN21a was only fitted to Manchesters. The FN64
(derived from the FN60 fitted to Blenheims) was fitted to early
Lancasters, and refitted to four of 5 Group's squadrons in June 1944 for
daylight raids (replacing the H2S scanner).

Lowering the dustbin under-turret apparantly produced a marked change in
trim, and a gunner described the experience of manning one as like
getting into a refrigerator with the lights out.

All accounts seem to agree that the only successful ventral defence
mounting was the Sperry ball turret.