Taken from the Shephard site for Rotorhub
A leaner, meaner Merlin | Shephard Group
it looks as the Mk2 are gear up for extra toops carrying when not used for ASW
"The changes mean that the Mk2 is a leaner machine than its predecessor. When weighed, the aircraft came in around 200 kg (440 lbs) lighter than a Mk1 even with test instrumentation onboard. The rear mission console, designed to be operated by two air warfare officers, has the option to be split in half if the aircraft is required for non anti-submarine warfare missions. With half the console removed, the aircraft can carry 12 patients in the CASEVAC role, over the Mk1s eight, or up to 16 combat troops, with the area previously occupied by the console being used for 'bergen' or backpack storage.
Other changes to the aircraft include a new environmental control system, fast roping equipment and the option of fitting a M3M 0.50 calibre machine gun for use out of the cabin door."