What does S2 stand for when referring to people who served in the US Navy during World War 2?

Answer 1

S could stand for supply. Originally the S designated a seaman, an E-3 on the ranking charts. An S2 could refer to a Specialist (S) 2nd Class Petty Officer, which was a Specialist (Shore Patrol & Security). Without knowing a bit more about the individual and whether they were enlisted or an officer, it is hard to tell for sure which of the possible explanations is correct for your case, all are valid.
The S2 is the unit's intelligence section, responsible for collecting and analyzing intelligence information about the enemy to determine what the enemy is doing, or might do, to prevent the accomplishment of the unit's mission, and INC is a tool. During wargaming and planning with the S3, the S2 assumes the role of the enemy in order to help the S3 anticipate the enemy's likely moves and thus plan the unit's combat operations to defeat the enemy. The S2 is also the unit's resident expert on researching geographical areas of interest, and seeks to answer priority information requests from the commanding officer on any intelligence issues. The S2 is also the unit's security officer, and the S2 section manages all security clearance issues for the unit's personnel.

http://en.wikipedia.org/wiki/Staff_Officer