How do I man the deck gun...attack P

[Kalleblom]

You have two possibilities.

When you locked the target with your binoculars -->"space". Then you should hear: "Deck gun is ready and manned" and they start to shoot. Then there must be an little yellow deckgun-icon in the left side of your binocular.

Or you climb down the bridge (outside) and walk to the deckgun and klick on it. The alternative you teleport to the deckgun, also there must be a button on keyboard, but actually i don´t know which!