The P-3 could launch Harpoons to good effect.
Think about the big picture, you're not going to launch an F-15 to fire AIM-7's at an aircraft carrier. That would be a waste of time and resources.
Rather, instead of hoping for "one platform, one shot, one kill", focus on a multi-layered attack using a mix of aircraft and missiles.
In LWAMI 3.11, they included the B-52 as a US air asset. This sounds odd at first since DW is primarily a Naval sim, but the B-52 could carry (and launch) up to eight Harpoons. P-3's and B-52's could be a very effective strike force when they worked together. Both planes had tons of loiter and search time and they carried enough Harpoons to get your attention.