UBoat upgrades---where?

[pcelt]

Where and how do you try and upgrade your UBoat when in the bunker.
Others have referred to this but I cn see no button or menu when back in the bunker.
Thanks for any enlightenment

[Nisgeis]

There's a man next to the man who gives you your missions. Press the ALT key to make him get a highlight. Talk to him and he'll sort you out.