Your Dad's duty was as or more dangerous than most might think. Merchant ships were prime targets, dangerous duty transporting men and equipment. These men do not receive full military benefits. Some for service during specified years and operations.
I have a friend who turns 100 Jan 12. The services wouldn't take him for some medical reason, so he went in the Merchant Marines. His merchant ship was torpedoed and sunk and they were in the water three days. Gave him a leave, then he went out on another ship. He gets some Military benefits, but not all that I get.