Because it is an air-to-ground weaponized variant of the NA-88 Cygnus Buccinator, the added weight of weapons makes the Little Nellie a tad too volitile for takeoff on land and thus is meant only for taking off, and landing, on water.
Instructions:
This is not your typical water takeoff...Before you power up the throttle, raise the landing gear. Then ***slowly*** bring the throttle to ~60%. When the tail raises so that the horizontal stabilizers are parallel with the...
...surface
of the water, gently pull back on the stick and, when you become airborne, crank the throttle to 100%.
Landing on water is a lot easier in this aircraft because the entire main fuselage is buoyant. In fact, you can dive into the water at 450MPH (~725KP/H) and simply float back up realatively unscathed. It is far safer however, to land like a normal water landing. You can land normally at 100MPH and skip along the water like a flat stone until you stop.

Cruzing Speed is around 60%~70% throttle.