The process of building airborne forces in 1941 led to a requirement for an air portable 105 mm howitzer.

This led to a requirement for a new trainer aircraft of the tractor configuration.

The increased German air traffic in the 1920s led to a requirement for a larger passenger transport aircraft.

This connection and an increase in barge traffic led to a requirement for more water.

However, by 2005, rising costs had led to a new requirement of £238 million against a cost of £325 million.

This leads to a requirement that hyperdocuments be self-contained.

This led to a new requirement that all designs had to undergo extensive water tank testing.

This leads inevitably to a requirement for typewriter ribbons.

This led to a requirement for very fast, well-armed vehicles.

This eventually led to a formal requirement being issued in 1976.