49 years ago on Monday, the M*A*S*H episode Abyssinia, Henry was broadcast, in which the commanding officer of the 4077th Lieutenant Colonel Henry Blake was killed off the show off-screen, the only major character to ever be killed off the series, with the episode ending with Radar’s memorable line:

“Henry Blake’s plane was shot down over the Sea of Japan. It spun in. There were no survivors.”

In order to keep the realism of the scene, the entire cast (Except for Alan Alda) didn’t find out about the decision to kill Blake until learning there was one additional scene to be filmed in the Season 3 finale, without rehearsal and in only one take.

The operating theatre scene.

Larry Gelbart, who directed the episode, later wrote this about the episode, specifically the final scene, in his 1998 book Laughing Matters:

Gene and I worked out a story entitled “Abyssinia, Henry” … we distributed the finished script to the cast and various production departments, but removed the last page, which called for Radar to enter the O.R. and read a Defense Department communiqué that informs everyone that Henry Blake, who had been discharged and was flying back to his family in the States, had gone down in the Sea of Japan. “There weren’t no survivors,” he concludes.

I kept that one last page under wraps, locking it in my desk drawer. The only cast member let in on the secret was Alan Alda, by then clearly the star of the series. We planned the production schedule for this episode so that the O.R. scene would be the last one shot.

There were, in fact, two O.R. sequences in that show: one at the top of the show, in which Henry is informed by Radar that he, Henry, is going home, that he has received his discharge orders, whereupon everyone in the room breaks into raucous song; the second, of course, was the final scene in which Radar enters to read the communiqué announcing Henry’s death. After we shot the first scene, the one in which Henry gets the good news, the cast and crew, understandably, began to wrap, pulling the plug on the episode and for that matter, the whole season…..

Later on…

We returned to the set. For once I said “Action” instead of “Cut.” We began to shoot the scene. Gary was unbelievably touching as he entered the busy O.R. and read the message to all the doctors and nurses. Extras in the scene, performers who had been with series since day one, reacted with a kind of heartfelt sincerity that was stunning — their performance was based on their real surprise and lingering shock, their awareness of how much Mac meant to them.

The crew, hearing of Henry’s death for the first time as the cameras were rolling, stuck to their chores; they did all one could ask of them.

Unhappily, there was some sort of technical glitch. Either the boom mike or a light or whatever could go wrong did, and we had to shoot it again. I was heartsick. Gary would never be able to do a second take as beautiful as he did the first. I still knew nothing about directing. He was better. And on the second go, a totally unexpected thing happened.

After Gary finished reading his message, there was a hushed silence on the set as B.J.’s camera panned the stricken faces of the cast, and then someone off-camera accidentally let a surgical instrument drop to the floor. It was perfect, that clattering, hollow sound, filling a palpable void in a way that no words could. I could not have planned it better; I wish I had — whenever I happen to hear it again, I marvel at how perfectly it fit.

Still, it wasn’t exactly a secret, because the Chicago Tribune had revealed exactly what was going to happen on January 20, and Blake’s fate was still being spoiled in newspapers shortly before the episode went to air: