I can press the letter F to move my bridge forward, but I have to click the BACK button on the screen to move my bridge back. It would be nice if I could press the letter B to move it backwards. That has to be the single most annoying feature about the game for me.
The problem is the hot key isn't labled on the screen.
And...
R is fo<B>r</B>eward and F is back... looks OK on the keyboard, but if you're thinking about the letter it's a little confusing.
Try hitting the "R" key (and remember, when all else fails, read the manual

).