The
B-1 is a remarkable bird but it has to fly. Going straight up takes it
into
an area it's not designed to operate at. This is one bird I wouldn't want
to be within 10 miles if it were to stall with less than 20,000 feet
involved.

As he said, for a short period of time. Start with a 500 kt pass pull
to the vertical, unload a bit and recover when airspeed reaches that
point below you don't want to go. Thrust to weight limits would apply
should you wish to accelerate vertically (or start at zero airspeed
There may be some other reason that a bone can't go vertical for a bit
but it's not lack of energy.

Pugs

good info can be found here

http://www.fas.org/nuke/guide/usa/bomber/b-1b.htm