Sailor Steve: Here's one way to go about it. A map image sent from the clipboard to MS Paint. Not my favorite graphic program but probably the one most people have. You set text in MSPaint by drawing a box that can either transparent or your choice of color and then start typing in the font you want. You can scale the box by grabbing at one of the corners. Takes a bit of trial and error to find out if the box is wide enough to accomodate the type. I might be doing it wrong too. I haven't used Paint in ages...
Winters: Yeah I like to sail all the way back to port too. For me a big part of the challenge of being a U-Boat captain later in the war is getting across that home stretch in the Bay of Biscay to your port without getting nailed by planes from Coastal Command. Plus, being able to teleport home means you gain an unrealistic radius of action since you really never have to worry about having enough fuel to get back. Of course, everyone is free to play in the style they find works best.
Dowly. Thanks fer asking They're all yours!

Being a budding Photoshop guru you should have no trouble knocking out the white background on these.