From Wikipedia"
The VB became the main production version of the Mark Vs. Along with the new Merlin 45 series the B wing
was fitted as standard. As production progressed changes were
incorporated, some of which became standard on all later Spitfires.
Production started with several Mk IBs which were converted to Mk VBs by
Supermarine. Starting in early 1941 the round section exhaust stacks
were changed to a "fishtail" type, marginally increasing exhaust thrust.
Some late production VBs and VCs were fitted with six shorter exhaust
stacks per side, similar to those of Spitfire IXs and Seafire IIIs; this was originally stipulated as applying specifically to VB(trop)s.
After some initial problems with the original Mk I size oil coolers, a
bigger oil cooler was fitted under the port wing; this could be
recognised by a deeper housing with a circular entry. From mid-1941
alloy covered ailerons became a universal fitting.
A constant flow of modifications were made as production progressed. A
"blown" cockpit hood, manufactured by Malcolm, was introduced in an
effort to further increase the pilot's head-room and visibility. Many
mid to late production VBs - and all VCs - used the modified, improved
windscreen assembly with the integral bullet resistant centre panel and
flat side screens introduced with the Mk III. Because the rear frame of
this windscreen was taller than that of the earlier model the cockpit
hoods were not interchangeable and could be distinguished by the wider
rear framing on the hood used with the late-style windscreen.
Different propeller types were fitted, according to where the
Spitfire V was built: Supermarine and Westland manufactured VBs and VCs
used 10 ft 9 in (3.28 m) diameter, 3 bladed de Havilland constant speed
units, with narrow metal blades, while Castle Bromwich manufactured VBs
and VCs were fitted with a wide bladed Rotol
constant speed propeller of either 10 ft 9 in (3.28 m) diameter, with
metal blades, or (on late production Spitfires) 10 ft 3 in (3.12 m)
diameter, with broader, "Jablo" (compressed wood) blades. The Rotol spinners were longer and more pointed than the de Havilland leading to a 3.5 in (8.9 cm) increase in overall length. The Rotol propellers allowed a modest speed increase over 20,000 ft (6,100 m) and an increase in the service ceiling.
A large number of Spitfire VBs were fitted with "gun heater
intensifier" systems on the exhaust stacks. These piped additional
heated air into the gun bays. There was a short tubular intake on the
front of the first stack and a narrow pipe led into the engine cowling
from the rear exhaust.
The VB series were the first Spitfires able to carry a range of
specially designed "slipper" drop tanks which were fitted underneath the
wing centre-section. Small hooks were fitted, just forward of the
inboard flaps: when the tank was released these hooks caught the
trailing edge of the tank, swinging it clear of the fuselage.
With the advent of the superb Focke Wulf Fw 190 in August 1941 the Spitfire was for the first time truly outclassed,
hastening the development of the "interim" Mk IX. In an effort to
counter this threat, especially at lower altitudes, the VB was the first
production version of the Spitfire to use "clipped" wingtips as an
option, reducing the wingspan to 32 ft 2 in (9.8 m).The clipped wings
increased the roll rate and airspeed at lower altitudes. Several
different versions of the Merlin 45/50 family were used, including the
Merlin 45M which had a smaller "cropped" supercharger
impeller and boost increased to +18 lb. This engine produced 1,585 hp
(1,182 kW) at 2,750 ft (838 m), increasing the L.F VB's maximum rate of
climb to 4720 ft/min (21.6 m/s) at 2,000 ft (610 m).
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