... and worst of all, you won't see much of a change sometimes when the light does light up. So lock on a target (as THEBERBSTER says), just like you're going to shoot a torpedo at it, but instead you are just going to take a picture. Click on the button whether it appears to be lit up or not. It just might work...
Most of the missions in stock do work, but can be finicky (besides being beyond fantasy on a few of them). You have to make a note as to what your instructions are from the orders before you go, since there will sometimes be a clue as to what you're supposed to take a picture of (if not naming a specific ship), and possibly when to do it date-wise. Here's what you probably got for Hiroshima:
Intelligence has requested a update on the enemy presence in Hiroshima harbor. Recon the area and, if possible, infiltrate the anchorage and photograph any enemy ships encountered.
So you can basically take a picture of anything "enemy" at just about any time frame. Some of the missions that don't work, are missing their "target" ship(s). But some of them, the "target" ship(s) are hidden behind other ships, and you just have to go in a little further, or perhaps in a slightly different direction to get them locked into your periscope.
Digging a little deeper into this particular mission, just as an example of how "they" do it, here's a picture from the Mission Editor of this particular "Mission", with the Map Zone Properties page open:
Notice how there are no ships in the mission itself? Only a map zone, and it is 7km in size. Your boat has to be within that circle. The "target" ship has to be within that circle. There does not appear to be a minimum number of pictures to take, just 35 points worth, so a big ship should be enough points for the Objective. Now, where do those "target" ships come from? Why, the game, of course. With just the Jap Harbor Traffic layer added into the mission:
Each of those little yellow squares is at least one ship. Granted, not all of them will be there at one time, since they might only spawn 35% of the time, or maybe 75% of the time. But generally speaking, you should have at least one third to one half of those yellow boxes as ships when you get in there. You can see though, that you do have to get in kind of close. Notice though that the BB and DD to the left of the circle are OUTSIDE the circle and would not count as "targets"...
This is where a photo mission into Hiroshima Harbor most likely was never requested of a submarine. That is a ~LONG~ way into that area, in mostly shallow water, basically infested with patrols and other ships... But it can be fun to try to do it... Just don't try this in TMO or FotRSU where you'd probably run into either a minefield or an anti-submarine net at least once on the way into there...
