My grandfather had this picture in his photo album and we're not sure if he was on this ship or not but were wanting some more info on it if available. He was stationed in Alaska during WW2 and took part in the Aleutian Islands Campaign.
This ship is the Gilliam-class USS Cortland (APA-75, rendered on the hull as ^(PA)75). It was a troop transport ship designed for staging an amphibious assault (with the use of the attack craft you see next to it). NavSource has an entry about the Cortland, which seems to include a low-res copy of the photo you've presented.