Differences in Aviators

[Niner Delta]

Naval Aviator

On a carrier, the Naval Aviator looks over at the Catapult Officer
("Shooter") who gives the run up engines signal by rotating his finger
above his head. The pilot pushes the throttle forward, verifies all
flight controls are operational, checks all gauges, and gives the Cat
officer a brisk salute, continuing the Navy/Marine tradition of asking
permission to leave the ship. The Cat officer drops to one knee while
swooping his arm forward and pointing down deck, granting that
permission. The pilot is immediately catapulted straight down the deck,
before catapults many Naval pilots lost their way before
reaching the end of the deck.

Air Force Pilot

We've all seen Air Force pilots at the air force base look up just
before taxiing for takeoff and the ground crew waits until the pilot's
thumb is sticking straight up. The crew chief then confirms that he sees
the thumb, salutes, and the Air Force pilot then takes off. This
time-tested tradition is the last link in the Air Force safety net to
confirm that the pilot does not have his thumb up his ass.

Army Aviator

If you've ever seen an Army helicopter pilot preparing for takeoff, you
will note that the pilot gives the ground guy a thumbs up before he is
given hover and takeoff signals. There are two theories about the origin
of this gesture. One is that it is to show that the pilot has identified
which of his fingers is the thumb so that he will be able to properly
operate his controls. The most compelling theory says that this is to
show the ground crewman that the pilot indeed knows which direction is
up.

[Karl/Pa.]

Thats about right.