By 1940 it was clear that the traditional Mk II ‘Tommy’ helmet could be improved upon. It’s broad brim made it very effective at protecting the head from shrapnel bursting above, but offered little protection to the temple or the base of the skull. A new design was prepared and trialled in 1941 before mass production began in 1943. The new helmet, known as the Mk III, was issued to the assault waves on D-Day and served alongside the earlier pattern throughout the war.

The new design was quickly nicknamed the ‘turtle’ due to the shape of the helmet that was flared out all around, offering about 15% greater side protection and 11% greater overhead protection than its predecessor.

I bought this example from Soldier of Fortune many years ago and I have been informed that the green, rough paint finish is indicative of it having been refurbished by the Irish Army at some point in the post war period, this may also apply to the liner, which I do not believe is original:

It is however similar in design to the original Mk III liners which were identical to the earlier Mk II liners with a cruciform rubber pad in the crown and five leather segments around it to support the helmet on the head. Unlike the later Mk IV helmet, the Mk III still used a small brass bolt and nut to hold the liner into the shell:

The chin strap is attached with two bales, one on either side of the shell. These are positioned higher up the shell than the later Mk IV which made the helmet unsteady when carrying water in the shell:

The Mk III helmet was slowly rolled out to the British Army during and after World War II, however such large quantities of Mk II helmets had been produced that these remained in service, alongside the Mk III well into the 1950s, by which time the Mk IV had been introduced and would slowly supplant both earlier designs.