Jakob Hammer joined the U.S. Navy just after the Japanese invasion of Pearl Harbor. He served on the U.S.S. San Francisco upon completion of his Basic Training and Gunner's Mate School. After spending time there, he found life aboard the ship to be a bit boring, and so he transferred his services over to the UDT program in hopes that it would be more of an exciting environment. He participated in the landing on Tarawa where he was severely wounded in a manner which gave him his code name, Grenade Bait. While sitting on a crate of grenades, a Japanese infiltrator tossed a grenade of his own which rolled right up to Hammer and exploded. As a result of the explosion, he lost his left eye and suffered extensive shrapnel wounds to his body. The only way the doctor's though he could be saved was to try out the Navy's experimental Super Sailor Serum on him. The experiment was a great success and even exceeded the government's expectations. It even worked better than the Army's serum by imparting Might, Constitution, Reduced Aging and Invulnerability. Since then, Grenade Bait has fought in every major American war as an agent of the U.S. government. After the fall of Communism in the 1990s, he was placed on inactive reserve and is now subject to recall at any time the country requires his services!