General Geiger's HQ, Guam
painting by Robert Greenhalgh

1946

Lieutenant General Geiger Warns that Atomic Weapons Threaten Amphibious Assaults*

In July 1946, the Navy supervised two atomic tests at Bikini Atoll in the western Marshall Islands. These tests, dubbed Operation Crossroads involved more than 70 surplus ships and craft anchored in Bikini lagoon, and were mainly designed to evaluate the effect of atomic weapons on warships.
Operation Crossroads examined the effects of both air and underwater explosions. During Test Able, which took place on 1 July, a bomb was detonated at 518 feet above the surface of the lagoon. Five ships sank, and the resulting blast, shock, and heat caused physical damage to almost 80 percent of the warships of the target fleet. Officials also estimated that, had the ships been manned, radiation effects would have incapacitated the majority of any crewmembers caught topside.
Test Baker was conducted on 25 July. It involved an underwater burst that sank nine ships, including the aircraft carrier Saratoga (CV 3) and two battleships. The mist that resulted from the burst also led to the widespread radioactive contamination of surviving ships and much of the atoll.

Lieutenant General Roy S. Geiger, Commanding General, Fleet Marine Force Pacific was the senior Marine present at the tests. Immediately afterward, he dashed off a correspondence to the Commandant of the Marine Corps, General Alexander Vandegrift, summarizing his view of Crossroad's implications for the future of amphibious operations - and the Marine Corps itself.
To Geiger, the test's results necessitated a complete review of amphibious doctrine. A future enemy would likely have large numbers of atomic weapons at their disposal. Given that, World War II-style amphibious operations such as those that had occurred at Normandy or Okinawa - operations that depended upon mass and the concentration of forces - would no longer be feasible. An assembly of warships, amphibious shipping, and small boats off a hostile coast would be a perfect target for atomic attack. Instead, Geiger believed that "future amphibious operations will be undertaken by much smaller expeditionary forces, which will be highly trained and lightly equipped, and transported by air or submarine." In addition, these assaults would be accomplished "with a greater degree of surprise and speed that has ever been heretofore visualized."
General Vandegrift was not as convinced as Geiger that atomic weapon employment would become a common element of military operations. Nevertheless, he felt compelled to study the problem thoroughly. He appointed a special board consisting of Major General Lemuel C. Shepherd, Major General Field Harris, and Brigadier General O.P. Smith and charged them with determining how these weapons would affect future amphibious assaults. In turn, much of the board's supporting research was conducted by officers from Marine Corps Schools, particularly Colonels Merrill B. Twining and E. Colston Dyer.
The board reported back to Vandegrift in December 1946. Their review stated that the Marine Corps would indeed have to make fundamental changes in the way it conducted amphibious assaults if it was fighting a nuclear-armed foe. They were confident that a dispersed amphibious task force approaching an enemy coast could reach its objective without significant damage. Likewise, they believed that an enemy would not employ atomic weapons against a U.S. landing force once it was ashore and engaged in combat unless they were willing to obliterate their own troops as well. However, the board emphasized that waves of slow, relatively closely packed landing craft and amphibious tractors moving Marines to the beach would be a tempting target for atomic attack. Had Japanese forces at Iwo Jima had these weapons, the board observed, they could have destroyed the two Marine divisions involved in the assault as they moved from ship-to-shore.
To avoid this, the board members recommended that the Marine Corps develop a method by which its units could be airlifted by helicopters from the decks of their amphibious warships to weakly held points behind the enemy's coastal defenses. These air-mobile units would be able to rapidly engage and mix with hostile forces on the ground and would open the designated landing beaches for reinforcements carried ashore by landing craft or even fast seaplanes. An assault of this nature would deny the enemy a lucrative target for an atomic strike but would also permit the landing force to mass its efforts at decisive points.
General Vandegrift concurred with the board's conclusions. However, there were many obstacles - and much knowledge to be gained - before the vision first promulgated by the board was realized. The most obvious obstacle was that fact that the Marine Corps did not operate helicopters in 1946. Moreover, helicopters at that time were generally small limited-capability aircraft that could carry only light payloads.
In addition, the plan was not well received in all corners of the Navy and Marine Corps. Before they could even acquire helicopters, Marine proponents of the new concept would have to convince the Navy to carry these aircraft on board its ships, something the Navy planners had not expected to do. Within the Corps itself, there were some who perceived helicopters as a threat to both fixed-wing close air support aircraft and ground-based artillery.
Despite these challenges, vertical envelopment and dual air and surface amphibious assaults eventually became second nature to the Marine Corps and the Navy. Though their forces never fought in a nuclear environment during the Cold War years, Operation Crossroads and the possibility of atomic combat ultimately led to significant changes in the way the U.S. naval services would conduct all amphibious assaults.