What is your favorite military prank?

I was working in Munitions Inspection and we were performing annual inspection on several lots off grenades. I had a spare pin and everyone was concentrating on the task at hand, when I held up the pin and asked if anyone had seen my grenade.
Jet engine mechanics used to send new guys to the engine test cell to perform an echo check on an F-4. They had them hollering into the intake of an aircraft to check the echo.
I walked into my shop and there were several young troops taking a break. I asked if anyone knew anything about electronics. (Keep in mind that electronics looked like a great career opportunity) When one of the guys raised his hand, I told him to get the buffer and buff the floors.

I was on Submarines. We were leaving Bahrain after operating in the area for about 6 months. While we were in port, I bought an alarm clock in Manama that sounded like the Muslim call to prayer. I took the alarm clock and set it for just a few hours after we were going to dive, cranked the volume to 11 (lol), and then took EB Green (duct tape) and taped it up so that only the speaker was open (and so you couldn't get to the snooze).

I went into the Goat Locker (the Chiefs' berthing), opened an access panel in the outboard, taped it on the backside of the bulkhead (wall), and closed the access panel. A few hours after we dived, read: just a couple of hours after the chiefs who weren't on watch hit the rack, that alarm went off. I understand they tore the entire Goat Locker apart trying to find it, lol...

On my next watch, I was driving the boat at the Helm and my COB (Chief of the Boat, the Senior Enlisted Advisor) was my Diving Officer. He said to me, "Glade, I know you've got your ear to the deck plates. Do me a favor and find out who the F' set that MF." I replied "Aye, COB," lol...

As I was leaving the boat (roughly 6 months later), I came clean to him, lol...

Duct taping the watch officers shoes to the shaft.

When I first arrived on my ship, they told me to run to DC Central and ask for a DC Punch. I didn't fall for it, but I went along with it. Kinda.

I have heard about the P U Fifty Five Yankee authorization form.

..or the one I loved to pull. Screenshot the desktop and set it as the wallpaper.. then hide all the icons and taskbar.

We were guarding an ASP up in Wash State, had a crew of like 12 stuffed into a GP ultra super duper small tent while our OIC had a GP Large all to himself , at dusk ,just as figures start to blend into the shadows he would attempt to sneak up on us in an attempt to catch us slacking> the 1st thing we did was took 550 chord and tent stakes and made trip lines across the area he used EVERY night,like clock work, ohhh shadow thirty came and so did a tiny little shadow ( he was maybe 5'3"on his best day), the shadow disappeared behind the usual tree and when he came yelling from behind it he made maybe 3 strides before laying himself out flat on the forest floor, got up bitching and stumbled back to his GP Large, not having extracted enough pleasure at his expense we waited till we were sure he was asleep, grabbed our artillery, hand grenade and what ever other simulators we could find and set out for his tent. His tent was completely empty save a field table with paper work spread across it ,a field chair and his cot, his uniform was draped over the back of his chair and he was nestled into his comfy fart sack with just the tip of his nose sticking out. There were 7 of us I believe, all pulled the pins and released our simulators, a few chose to stay ( I was one of them) The 1st one to go off was close enough to the table top to create an eruption of forms and what ever else he had on the desk, He was trying to get out of the sleeping bag while simultaneously looking for cover, trying to pull his clothes on and run, not a graceful combination !!! Ohhh and I will add he screamed like a girl !!! By the time he got his senses together and I think changed his underwear, we were all back in our GP xxxxx small in our bags and snoring like champion bears. He barged in screaming all kinds of wild crap and we just played dumb! His stupid antics of John Wayne stopped and we enjoyed the rest of our duty with just brief visits from him !!

On a previous deployment our shop had a thing for unattended CACs. Clear tape placed over the chip on a CAC, the victim then wondering why they couldn't log onto the computer. Another unattended CAC resulted in the victim having to follow the scavenger hunt clues to find it. Another CAC ended up a prisoner, soldered into a copper wire cage. And finally a water bottle cut in half, the CAC inserted, the bottle reassembled with some kind of glue, filled with water and frozen.

There are so many out there.squelch juice,chemlight batteries,ID10T,gridsquares,flightline,check for softspots on armor vehicles,exhaust samples and the list goes on.

An old Gunny tank driver I knew said in Desert Storm they would collect bags of excriment and dump them in a comrads tank then sit on the hatch so they couldn't get out. At 120 degrees it got rather stinky so I here.

Well of course you can't beat the ol' find the camera (or camera phone in modern times) and snap a pic of everyone's junk!

MP prank: "Go and secure Building One" while watching them continue to drive pass the Post Flag Pole forever.