According to Gordon L. Rottman's U.S. Marine Corps World War II Order of Battle: Ground and Air Units in the Pacific War, 1939-1945, a total of 669,108 Marines served in uniform during World War II, with the Marine Corps reaching its peak one-time strength in August 1945 at 485,113. If 669,108 Marines served during WWII with 21,242 of them dying in battle, the figure is roughly 3.17%, discounting roughly 4,700 non-battle deaths, so the figure of 3.7% seems solid.
The casualties in most division types will be heavily concentrated in those components routinely involved in face-to-face contact with the enemy;
| Unit type | F-series Marine division, 1944 | U.S. Army Infantry Division, 1944 |
|---|---|---|
| Infantry Units | 6,858 | 5,211 |
| Infantry Heavy Weapons Units | 609 | 640 |
| Engineer Units | 904 | 637 |
| Pioneer Units | 745 | -- |
| Reconnaissance Units | 127 | 149 |
| Armored Units | 630 | 720 (not organic) |
Extremely high casualty rates in frontline infantry units was the norm for nearly all involved nations during WWII. Using the U.S. Army's Infantry Branch as an example;
| Deployed overseas | Total battle casualties | Deaths among battle casualties | KIA | DOW | Died while MIA | Died while POW | WIA | MIA | POW |
|---|---|---|---|---|---|---|---|---|---|
| 757,712 (officers) | 33,538 | 8,788 | 7,002 | 1,185 | 79 | 522 | 23,581 | 286 | 2,669 |
| 757,712 (enlisted) | 627,521 | 134,174 | 110,639 | 18,428 | 1,716 | 3,391 | 447,795 | 15,544 | 53,543 |
| Total | 661,059 | 142,962 | 117,641 | 19,613 | 1,795 | 3,913 | 471,376 | 15,830 | 56,212 |
I have copied several charts from Rottman's and Nofi's books below;
Casualty Statistics:
| Category | Number |
|---|---|
| Number served | 669,108 |
| KIA, DOW, MIA and declared dead, POW and declared dead or executed | 21,242 |
| WIA | 67,207 |
Casualties by Division:
| Division | Battle Deaths | Other Casualties | Total |
|---|---|---|---|
| 1st | 5,435 | 13,849 | 19,284 |
| 2nd | 2,729 | 8,753 | 11,482 |
| 3rd | 1,932 | 6,744 | 8,676 |
| 4th | 3,317 | 13,006 | 17,722 |
| 5th | 2,113 | 6,450 | 8,563 |
| 6th | 1,637 | 6,590 | 8,227 |
Casualty Statistics by Operation:
Prisoners executed or that died after capture are designated by "[ ]"
Wounded in action figures enclosed by parentheses "( )" are included in the POW total
| Operation | KIA | DOW | WIA (and captured) | MIA and presumed dead | POW [executed or died] | Total |
|---|---|---|---|---|---|---|
| Pearl Harbor 7 Dec 41 | 105 | 7 | 71 | -- | -- | 183 |
| North China 8 Dec 41 | -- | -- | -- | -- | 198 [?] | 198 |
| Guam 8-10 Dec 41 | 4 | 1 | 13 | -- | 135 [5] | 153 |
| Wake Island 7-23 Dec 41 | 50 | -- | (44) | 6 | 349 [13] | 449 |
| Sea Duty^1 28 Feb-1 Mar 42 | 50 | -- | -- | -- | 24 [?] | 74 |
| Philippines 8 Dec 41-6 May 42 | 310 | 5 | (357) | 16 | 1,388 [490] | 1,719 |
| Midway Island 7 Dec 41-6 Jun 42 | 10 | 1 | 39 | 37 | -- | 87 |
| Guadalcanal 7 Aug 42-8 Feb 43 | 1,097 | 109 | 2,916 | 298 | -- | 4,420 |
| Makin Atoll 17-18 Aug 42 | 18 | -- | 16 | 3 | 9 [9] | 46 |
| New Georgia^2 20 Jun-16 Oct 43 | 153 | 10 | 415 | 58 | -- | 636 |
| Bougainville^3 27 Oct 43-15 Jun 44 | 352 | 88 | 1,249 | 291 | 1 [1] | 1,981 |
| Cape Gloucester/New Britain 26 Dec 43-1 Mar 44 | 264 | 50 | 815 | 124 | -- | 1.253 |
| Volupai-Telasea 5 Mar-25 Apr 44 | 12 | 16 | 133 | 9 | -- | 170 |
| Aviation^4 9 Feb 43-15 Mar 45 | 196 | 16 | 123 | 571 | 22 [?] | 1,029 |
| Sea Duty Jun 43-Mar 44 | 20 | 5 | 95 | 61 | -- | 181 |
| Tarawa^5 20 Nov-8 Dec 43 | 904 | 93 | 2,233 | 88 | -- | 3,318 |
| Kawajalein/Majuro 29 Jan-8 Feb 44 | 175 | 31 | 617 | 181 | -- | 1,018 |
| Eniwetok 17 Feb-2 Mar 44 | 181 | 38 | 568 | 39 | -- | 826 |
| Saipan 11 Jun-10 Jul 44 | 2,077 | 367 | 8,575 | 708 | -- | 11,727 |
| Tinian 24 Jul-1 Aug 44 | 300 | 65 | 1,921 | 3 | -- | 2,289 |
| Guam 21 Jul-15 Aug 44 | 1,156 | 395 | 5,365 | 17 | -- | 6,833 |
| Aviation^6 20 Nov 43-15 Aug 44 | 37 | 6 | 120 | 22 | -- | 185 |
| Sea Duty 20 Nov 43-15 Aug 44 | 13 | 2 | 58 | 4 | -- | 77 |
| Peleliu^7 6 Sep-14 Oct 44 | 1,050 | 250 | 5.450 | 36 | -- | 6,786 |
| Iwo Jima 19 Feb-26 Mar 45 | 4,554 | 1,331 | 17,272 | 46 | -- | 23,203 |
| Aviation^8 Feb 44-Jun 45 | 115 | 9 | 303 | 76 | -- | 503 |
| Sea Duty^10 Mar 44-Jun 45 | 65 | 9 | 150 | 63 | -- | 287 |
| Okinawa 1 Apr-22 Jun 45 | 2,699 | 519 | 15,667 | 20 | -- | 18,905 |
| Aviation^9 1 Apr-22 Jun 45 | 49 | 10 | 222 | 35 | -- | 316 |
| Sea Duty^10 1 Apr-22 Jun 45 | 98 | 1 | 118 | 12 | -- | 229 |
| European Theater 1941-45 | 4 | -- | 1 | -- | 4 | -- |
| Mediterranean Theater 1942-45 | 2 | -- | (2)/1 | -- | 4 | 7 |
Sources:
U.S. Marine Corps World War II Order of Battle: Ground and Air Units in the Pacific War, 1939-1945, by G.L. Rottman
Marine Corps Book Of Lists, by Albert A. Nofi
Administration of the Navy Department in World War II, by Julius Augustus Furer