From The Day of Battle: The War in Sicily and Italy, 1943-1944, Volume Two of the Liberation Trilogy, by Rick Atkinson (Henry Holt, 2007), Kindle pp. 507-509:
The newest units to join Fifth Army—the 85th and 88th Infantry Divisions, both in Keyes’s II Corps—were the first into combat of fifty-five U.S. divisions built mostly from draftees; their worth had yet to be proven. Four of six infantry regimental commanders in those two divisions had already been relieved, as Clark advised Marshall, “for a combination of age and physical reasons.”
There was more: the two British divisions still at Anzio remained so weak that both Truscott and Clark believed they would contribute little to any renewed offensive. The British Army since Salerno had suffered 46,000 battle casualties, with thousands more sick, yet replacements had not kept up with losses. Moreover, as Gruenther also noted, “Many British troops have been fighting for four or five years, and are in some cases pretty tired.”
Few British commanders disagreed. “Absenteeism and desertion are still problems,” wrote General Penney, back in command of the British 1st Division at Anzio after recovering from his wounds. “Shooting in the early days would probably have been an effective prophylactic.” On average, 10 British soldiers were convicted of desertion each day in the spring of 1944, and an estimated 30,000 “slinkers” were “on the trot” in Italy. “The whole matter is hushed up,” another British division commander complained.
Nor was the phenomenon exclusively British. The U.S. Army would convict 21,000 deserters during World War II, many of them in the Mediterranean. Clark condemned the surge of self-inflicted wounds in Fifth Army and the “totally inadequate” prison sentences of five to ten years for U.S. soldiers convicted of “misbehavior before the enemy.” A psychiatric analysis of 2,800 American troops convicted of desertion or going AWOL in the Mediterranean catalogued thirty-five reasons offered by the culprits, including “My nerves gave way” and “I was scared.”
A twenty-two-year-old rifleman who deserted at Cassino after seven months in combat was typical. “I feel like my nervous system is burning up. My heart jumps,” he said. “I get so scared I can hardly move.” Those symptoms affected tens of thousands, and added to Clark’s worries. “Combat exhaustion,” a term coined in Tunisia to supplant the misnomer “shell shock,” further eroded Allied fighting strength in Italy, as it did elsewhere: roughly one million U.S. soldiers would be hospitalized during the war for “neuro-psychiatric” symptoms, and half a million would be discharged from the service for “personality disturbances.”
All troops were at risk, but none more than infantrymen, who accounted for 14 percent of the Army’s overseas strength and sustained 70 percent of the casualties. A study of four infantry divisions in Italy found that a soldier typically no longer wondered “whether he will be hit, but when and how bad.” The Army surgeon general concluded that “practically all men in rifle battalions who were not otherwise disabled ultimately became psychiatric casualties,” typically after 200 to 240 cumulative days in combat. “There aren’t any iron men,” wrote Brigadier General William C. Menninger, a prominent psychiatrist. “The strongest personality, subjected to sufficient stress a sufficient length of time, is going to disintegrate.”