Why was the U.S. Marines given the Pacific as their primary task during WW2 while the Army was given Europe? Were there any efforts to use both the Army and Marines in the Pacific Front? Were there any drawbacks to this strategy?

by KevTravels
DBHT14

More US Army Soldiers were fighting in the Central Pacific, South Pacific, and China-Burma-India theaters than Marines. Anywhere the US had boots on the ground as it were, the Army was the largest share of them. The USMC was a comparatively tiny force, logistically, and doctrinally tied at the hip to the US Navy and the long theorized cartwheel of amphibious landings across the Central Pacific.

You may be interested in this post where I expand on the numbers, doctrine, and realities when it came to the USMC in WW2 and where it was used in large numbers. https://www.reddit.com/r/AskHistorians/comments/m02i52/i_read_earlier_that_in_ww2_us_marines_never/

jayrocksd

To add to u/DBHT14's point about how much the US Army was involved in the Pacific, the simple answer is that the Navy was leading the war in the Pacific for the US, and the USMC was part of the Dept. of the Navy. The US plan for the war quickly became Germany first with the Army taking the lead for the US in Europe and the Navy in the Pacific. While part of this may be because Army Chief of Staff George Marshall didn't want to argue with the irascible CNO ADM Ernest King, it also made sense due to the nature of the War in the Pacific.

King and Marshall actually had a good working relationship, but King also took every opportunity to send resources to the Pacific despite the Germany first policy, especially as the invasion of France was pushed back until 1944. He certainly wasn't going to release a resource such as the USMC which was specifically trained and equipped for the type of war that was happening in the Pacific theater. Nor would Marshall think of asking.

US military leaders had been thinking about what a war with Japan would look like since the Russo-Japanese war. While a few different strategies were considered, the strategy that eventually shaped the fighting had really been decided on by the mid-30s. This was the 3 phase plan of securing the eastern Pacific, island hopping across the Pacific through the Japanese Mandates and destroying the Japanese Fleet, then forcing Japan to surrender through blockade and bombardment. Decades before war broke out, it became very clear that the Navy would have primary responsibility in any war with Japan due to the vast distances across the Pacific. Which islands would be taken and which would be bypassed changed quite a bit, but the strategy stayed the same. Edward S. Miller in his book: War Plan Orange: The US strategy to Defeat Japan 1897-1945 provides a very detailed description of how this plan developed. You can also get a gist of the plan development in this talk from Peter Pellegrino, who is a wargame designer at the Naval War College.

TLDR: The USMC was part of the Department of the Navy, which was better suited than the army to take the lead in a theater that involved island-hopping across thousands of miles of ocean while simultaneously dealing with a very powerful Japanese Navy. In addition, 22 divisions of the US Army also fought in the Pacific.