Its first flight was in 1940, but problems with the design hampered development and it remained only marginally stable throughout the prototype phase.

For one, the technology is very much in a prototype phase, and little has been heard of it since its initial announcement.

The Sm3 had a long prototype phase before the main series was ordered, with reliability issues being brought up by the press from time to time.

There is a hoverbike currently in the prototype phase.

It's not a bad looking phone, even at the prototype phase.

A number of minor problems turned up during the prototype phase, and were dealt with over the next year.

During the prototype phase, the army asked for a gun with considerably greater capability.

The analysts presented their findings to Warnaco a few weeks ago and are now entering the prototype phase.

As such, it was never sold, or even got beyond the prototype phase.

No magazine-fed versions of the Berdan ever progressed beyond the prototype phase.