The Marine Corps trained the Navy U.D.T. teams when they wanted to get more training on beach sabotage so the Marine recon unit from 1st Div. went down to San Diego for cross training. This is when that pin was made up for the teams, and they called them Navy seals. The dagger was for sabotage up close work, anchor for coming from sea or Navy, and Eagle showing strength. The seals wanted a symbol that was bigger than the submariner's had so they changed to the trident that they have now to show they were a bad ass bunch. Hope this helps