I've positioned sirens in my airbase ( witihn the circular perimeter marker) but when the ju88s come to bomb my base, no sounds. The sirens are set up as red as they should be ( I guess) Anyone know what's wrong? Do I need lots of sirens or what?

One siren is enough. Just curious, but how are you testing to hear the siren? I mean, where are YOU, as the player?

Aviar

As sirens are red, check if you as a player is red and the Ju-88 are blue side.
One siren should do.

Ta for the replies. I'm in my plane ready for take off. Usually in other campaigns I've been able to hear the siren but I can't in my own mission

Place one Red siren near each end of the runway. When the Blue bombers get near your airfield, you should easily hear the sirens from your cockpit.

If you don't, I'm not sure what your problem is. You may have to adjust one of your sound settings.

However, if you can hear sirens in campaigns, then you may have simply set up your mission incorrectly. Double-check the mission.

Your plane should be Red. The siren(s) should be Red. The bombers should be Blue. Make sure you don't have any Blue objects on your base.

Aviar

Not sure if this will help, but did you designate the airfield as your home base...its worth a shot

The sound configuration should be such that you do have some volume on "objects".

Also, like Aviar suggests, it should be close enough to prevent your engine to drown out the siren.

Just out of curiosity, could you dump the contents of the .mis file here?

If you have a siren at the other end of the runway from where you are taking off, you won't hear it much at first until you hit the end of the runway. I usually put a few down along the landing strip so it sounds like the entire base is on alert.

Also, you may want to place an enemy plane close to the airfield to get the sirens to go off. In many of my missions I want the siren to go off before the planes arrive so I put a dummy enemy plane nearby and low (and have it do a kamikaze attack on an AA emplacement to get rid of it).