How quickly could Marines create helicopter air cavalry?

How long would it take Marines to turn an early helicopter into a form of air cavalry?

Probably very little time; crews would improvise with small loads first, then use the experience to demand larger purpose-built troop carriers.

Royal Marines and boarding parties would probably test troop carriage as soon as a helicopter proved reliable. Removing seats might fit four or more lightly equipped personnel inside, but the estimate concerns cabin space and does not establish an acceptable takeoff load. External or door-side carriage is also the kind of field modification an aggressive unit might try before formal doctrine exists. A successful experiment creates pressure for greater cabin volume, payload, and easier embarkation in the next design. Repeated operational improvisation can pull troop-carrying capability forward much faster than a paper specification alone.