The No. 2 Mk. 1 was single action/double action with a normal hammer.
The No. 2 Mk. 1* was the double action only version, with a bobbed hammer and no sear.
Additionally, the DAO modification was not done exclusively for armoured corps, as this could be done by armourers (and the hammer spur is less likely to be caught on a hatch than the butt). It would also not require eliminating the sear, which prevents it from being cocked if a standard hammer were installed. This alteration was done because of a doctrine change favouring higher volume of fire over carefully aimed shots.