NAG, represents 'Naval Armed Guard'. This was a unit consisting of US Navy Gunners, Signals, and Pharmacists Mates commanded by an Ensign or Lt. These Ensigns or Lts were subordinate to the civilian ships Capt. These USN personnel were assigned to merchant ships fitted with deck cannons and anti-aircraft weapons.

The t was a typo.

Thanks again for responding to my question. My Dad was often in Glasgow and Scotland as he was assigned to the Atlantic Fleet and convoyed the Atlantic and Murmansk Run. Even so he sailed around the world three times during WWII.

Regards,

Jake