I did a quick search for 'H-67 watch movement' and found a link with the following comments:-
In the mid 1960’s Hamilton began to supply the British military with watches which included the Hamilton 6B H-67 which were issued to RAF aircrew. These watches were produced to the same MOD specification as their more expensive and illustrious counterparts, the JLC and IWC Mark XI.
It is believed that only around 1,000 of the Hamilton 6B H-67 were ever produced which makes these watches extremely rare and highly collectible.