When I was a kid, the taunt “Your mother wears Army boots” had not yet gone completely out of fashion. But the razz packed no punch for me. I could respond, “Actually she wears Marine Corps boots, and she will beat the hell out of your mother.” She had indeed been in the Corps, where she met my father. They were both sergeants. In his later years, my dad was fond of issuing his own taunts to ex-officers of other branches of the military, things like “You were a colonel in the Army? That's like being a corporal in the Marines.”

They have both received their honorable discharge from this life, but I know my folks would have appreciated some of the stories in Mary Roach's new book, Grunt: The Curious Science of Humans at War. Particularly the one involving another Marine Corps sergeant, name of Robinson, and Captain Mark Riddle, a Navy research physician. Riddle's specialty is diarrhea: “I live and breathe this stuff,” he says in Grunt.

Roach, Riddle and Robinson discussed diarrhea over breakfast at Camp Lemonnier in Djibouti. (In Iraq and Afghanistan, 32 percent of respondents in a Riddle survey reported an incident of having been unable to reach a toilet in time.) Robinson complained about the minuscule amount of toilet paper included with combat field rations. Riddle noted that Navy personnel sometimes pack baby wipes. Robinson replied that Marines use pieces of their T-shirts. Roach writes, “Which possibly sums up the whole Marine Corps–Navy relationship.”

In her book, Roach takes a deep dive into military science and medicine and how even the simplest activities are complicated by the realities of combat or readiness for it. For example, most of us may take for granted being able to hear co-workers when collaborating on a task. But ears take a constant beating in the service—weapons and explosions, Roach writes, “are the biggest contributors to the $1 billion a year the Veterans Administration spends on hearing loss and tinnitus.”

A platoon's members might want to protect their ears with plugs or higher-tech devices but not at the expense of being able to hear commands and warnings. And so well-meaning audiologists do a lot of testing and try to come up with solutions for use in the field. But when a group of special-ops personnel was asked if an audiologist had ever done anything positive for them, the only reply, Roach says, was, “They fitted me for my hearing aids.”

A general or admiral has undoubtedly made a good decision or two. But Grunt touches on how thousands of men and women may be inconvenienced or endangered by some mucky-muck's whim, even about uniforms. “An Army chief of staff decided that black wool berets would be the headpiece of the Army Combat Uniform,” Roach writes, because he thought it looked sharp. After 10 years, the Army was finally able to get back to baseball caps, with their eye-shading visors and thinner fabric, which makes them cooler to wear and easier to jam into a pants pocket—attributes that are actually functional.

In the early 2000s the Army attempted to come up with a Unified Field Theory, not for physics but for camouflage uniforms: they wanted one pattern that would hide troops in the woods, city streets and the desert. The uniform designers and engineers came up with 13 patterns for testing. But before the results were in, a general went ahead and picked a pattern—one that was not even among the 13 agreed-on contenders. “The new camouflage performed so poorly in Afghanistan that in 2009,” Roach notes, “the Army spent $3.4 million developing a new and safer pattern for troops deployed there.”

Meanwhile the Navy currently wears blue camouflage as its working uniform. “I asked a Navy commander about the rationale,” Roach recounts. “He looked down at his trousers and sighed. ‘That's so no one can see you if you fall overboard.'”

Maybe some high-ranking officers should have followed their hearts and become fashion designers. The grunts would be happier, the officers would be happier and they might have come up with a thicker-ply T-shirt for the Marines.