The Other Side of the Postcard

[Ed note: This is a 1 cent postcard. Have you seen any of these lately?]
"Jackies from the U. S. SS Utah recovering a spent torpedo after target practice. A torpedo is like a small independent submarine. It is 21 feet long, 21 inches in diameter and is divided into six compartments. The first or front compartment contains damp gun cotton and detonator which explodes the torpedo when it comes in contact with anything solid, as a ship's side. Second, compressed air tank contains 1,350 pounds of air to drive the propellers. Third, balance compartment from which project horizontal planes. Fourth, engine compartment containing turbine type motor drives by compressed air. Fifth, buoyancy compartment holding enough air to keep torpedo from sinking and making it easily propelled. Sixth, gyroscope compartment to insure its continuance on the course aimed. The torpedo also has horizontal and perpendicular rudders which may be set at any angle, and strong twin propellers."
Not being ordnance oriented we "zeroed in" on the first word - "Jackies." Having "one foot or the other" in the Navy for more than 61 years this came as a new term. Where in the heck did that expression come from? This e-mail reply from Shipmate James Oberto:
"You wanted to know what a Jackie is...well, a friend of mine told me; the British called sailors Jack Tars...it seems they used tar on their pony tails way back when and they became known as Jack Tars..shortened as the Brits often do..to Jackie...Ain't you glad you asked? Jim "O"...not a Jackie...just a Swabbie"