Hello, I answered. A commanding voice said you WILL be at Oxnard airport tomorrow at 8am. You WILL be prepared to repair the system that YOU built and isn't working. We have tens of billions of dollars worth of naval ships off the coast of the Channel Islands and YOUR system isn't working!!!
That was the president of the company that I had been consulting for. Backing up a few months I was called in to help with a project. They had purchased some surplus military equipment along with a complete set of drawings. This was a laser rangefinder system for a now defunct anti-aircraft tank system called Sgt York (named after a WWI soldier).
I was asked if I was familar with this laser system. I said I was. I pointed to the stack of drawings and asked them to pull out one. It had my signature as the project engineer from early in my career working for a defense contractor. My customer had a contract to improve the accuracy of the rangefinder by using a better receiver with a faster clock timing device. I was never told what the goal of the project was because it was classified, but I suspect it had something to do with tracking ship movements by looking at the wake.
Not knowing what to expect I packed a set of tools, got up early and dutifully drove to Oxnard airport some 80 miles from my home. When I arrived I was told that I would be flown by helicopter to San Miguel Island about 50 miles off the coast. I was given a briefing on how to stow and retrieve my gear from the storage compartment because the pilot would not exit the aircraft upon landing.
The weather was cold and dreary with a low ceiling. We reached the island and it appeared to me that my feet could almost touch the tops of the trees at the top of the ridge. We landed, I retrieved my gear and instinctively ducked down below the spinning rotor even though it was far above my head. I was met by a driver who took me to the test site on a cliff overlooking the channel.
"My" laser rangefinder was mounted on a tripod near the back of a box truck. I took one look at the system and knew instantly what was wrong. The new receiver required bipolar supplies at +/- 5 volts. The Sgt. York system ran off +/- 12V. I had added 3-terminal regulators to drop the voltage. Because this was a test system to be used just once, the added circuitry was not pretty. The TO-220 regulators were mounted to a perf-board sticking up into the air. Someone didn't like the looks of that and put a screw through the tab which grounded it to the case. For the positive side that wasn't a big problem other than a potential ground loop. However, for the LM7905 negative regulator the tab is the input voltage, not ground. The -12V supply was shorted to ground. Fortunately, the military spec'd power supply was overload protected. I removed the screw and the system powered up perfectly. Problem solved in less than a minute.
A light rain was falling and the temperature was in the high 40's. I had on only a light windbreaker and was freezing. I tried to warm my hands by a space heater in the back of the truck which was running off a generator. My companion said to me, I hope you brought a change of underwear. Why? The helecopter had flown back to the mainland and was unable to return due to weather. Oh crap! He got on the radio and then notified me that a ship was leaving in 10 minutes. But we were nowhere near the dock. We jumped in his truck and barreled down muddy dirt roads with no guardrails while I looked down the cliffs at the Pacific Ocean below. We made it to the dock just as they were casting off the mooring lines.
The seas were rough due to the storm and all other passengers remained topside feeling queasy. Fortunately, I had no such issues and went below where it was warm. After a few hours we arrived at Port Hueneme Naval Base. It was nighttime and the base was deserted at least near the waterfront. I was happy to be back on the mainland, but my car was at the airport. Since this was the 1980's there were no cell phone and no payphone was in sight. Fortunately, a fellow passenger on the boat volunteered to drive me back to Oxnard airport.
Moral of the story: Don't short the tab on a negative 3-terminal regulator to ground. Lesson learned.