As the fourth season opens, Hawkeye returns from a 3-day R&R pass in Tokyo to find Trapper has been sent Stateside. Hawkeye races to the airport but arrives just as Trapper's plane takes off. Too late to tell his friend good-bye, he in nevertheless just in time to welcome Trapper's replacement, Captain B.J. Hunnicutt. Once Hawkeye gets over his anger and disappointment, he realizes B.J. is a worthy ally and takes the newcomer under his wing. "The first thing you learn here, B.J., is that insanity is no worse than the common cold. You've heard of a military post? Ours is a compost. Only the wounded are new. The tedium is relieved only by the boredom. So pitch in, muddle through, pip-pip. Never mind the reason why, ours is but to do and not let 'em die."Then Colonel Sherman T. Potter arrives to take over command of the 4077. Not only are Frank and Hot Lips outraged that Frank has lost his command so quickly, but Hawkeye and B.J. know that an Army commander could spell big trouble for them. But then a single reminiscence from Potter puts the docs at ease: “Had a still on Guam in World War II. One night it blew up. That’s how I got my Purple Heart." Favors are being traded at the 4077th as Hawkeye and B.J. help a British soldier with an ingrown toenail in exchange for some scotch. Then they look for a replacement for their stolen microscope.