Yep twice. Another one related to navy ships but it wasn't somebody else taking the dive it was me. In my defense both ships were out to sea, so I like to say it was a pitch and roll that caught me off guard. But I digress. The first time I was a midshipman on a summer cruise. We were somewhere in the middle of the pacific, I jump on the TM and start in at a pretty good pace, just under about 10mph. Then the one hot girl on the whole ship starts on the treadmill right next to it. To this day I don't know what I did wrong, I didn't look left, I didn't look right, I don't remember catching the edge of the treadmill. What I do remember is hitting the treadmill hard and getting shot off the back on to a mat. Workout rooms on ships (even the big ships) aren't that big. The treadmills are literally rubbing up against each other sometimes. I remember the hot girl getting startled and grabbing the bars as I was hitting the mat. That being said, I've fallen plenty in other running scenarios when not on a treadmill, and I must say it didn't hurt that much. I hardly had a hint of a bruise. It's much better than hitting asphalt.
Anyway, I'd like to say that I jumped up on the treadmill and had some smart comment to throw at the one pretty sailor chick on the ship but I didn't. I just felt like an idiot and kept running.
My second time I was on an aircraft carrier in the Med during Operation Iraqi Freedom. This time, the boat, took a big roll. I was doing a workout that day and was probably at about 5:15 pace so I didn't have enough time to account for the sudden shift. Again, I was on my ass and out the back on to a mat. Everybody knew me as the guy that would "run fast" and "forever" on the treadmills. Well, after that I'm pretty sure I was known as the guy that fell of the treadmill. Now that room was packed with treadmills and bikes as it was a strictly aerobic workout room. There were a ton of people in there so this one also was a blow to the ego. Once again, I just got back up and started running again. What else could I do? And again, the treadmill made for nice fall. Didn't really suffer any ill effects from the crash.