And why would you call a Marine an “infantryman.” The corps is not infantry. He could have been a grunt but infantryman is not accurate.
You’ll have a hard time finding an MOS for “grunt” (0311). Every Marine is trained for infantry service and then sent to do whatever job needs doing. Air Wing, artillery, infantry, Admin., Supply... Force Recon was a specialized group chosen from the infantry and trained for their role. The Marine Raiders of WW II under the command of Carlson and Edson were deactivated and spread throughout the six Marine Divisions to train the newbies. Those units were no longer in existence at the end of the war.