Battle of Iwo Jima: Prelude

Battle of Iwo Jima

• Battle took place between February 19 and March 26, 1945.

Background

• Operation Detachment originated from a strategic planning conference in San Francisco from September 29 to October 1, 1944.
• Senior Pacific theater commanders and Joint Chiefs of Staff representatives attended the conference.
• Securing Luzon in the Philippines was the priority.
• General Douglas MacArthur advocated for securing Luzon.
• Although the target date for Luzon was December 20, the operation occurred on January 9, 1945.
• All strategic locations in Luzon were secured by March.
• After Luzon, the plan was to occupy the Bonins-Volcano group (including Iwo Jima) and the Ryukus (including Okinawa).
• The Bonins and Ryukus island chains run north to south in the Pacific, south of Japan's Honshu Island.
• The Bonins (Nanpo Shoto) and Ryukus (Nansei Shoto) were considered stepping stones to Japan and vital to Japan's inner defense.

Prelude

• The U.S. Army Air Forces gained prominence due to the strategic bombing campaign against Japan.
• A Japanese radar site on Iwo Jima provided early warning for U.S. air raids and served as a base for intercepting Japanese fighters.
• B-29s had to fly a longer route around Iwo Jima as a result.
• Securing Iwo Jima would provide airfields for fighter escorts and emergency landings for damaged B-29s.
• Post-Detachment, the assumption about Japanese early warning capabilities proved incorrect.
• Airfields' strategic utility was diminished by events elsewhere; the justification for the operation's high human cost is still debated.
• The U.S. Fifth Fleet (Admiral Raymond A. Spruance) was assigned to provide amphibious lift, gunfire support, air cover, and logistical support for Operation Detachment using Expeditionary Task Force TF-56, led by General Holland M. Smith, USMC.
• V Amphibious Corps (Major General Harry Schmidt, USMC) was primarily made up of the 3rd, 4th, and 5th Marine Divisions, the Army’s 147th Infantry Regiment, and support units.
• D-Day was set for February 19, 1945.
• Approximately 60,000 U.S. service members faced about 21,000 Japanese troops on Iwo Jima.
• Japanese defensive doctrine shifted after the Central Pacific battles of 1943 and early 1944.
• By June 1944, many senior Japanese officers considered Allied victory inevitable.
• Japanese commanders aimed to delay the Allies at the highest cost.
• The Japanese did not attempt to repulse Allied forces on landing beaches, as seen on Peleliu in September 1944.
• Assault troops faced a step-by-step battle of attrition, advancing through well-defended killing zones.
• U.S. air superiority led Japanese forces to construct mutually supporting, deeply sited, and heavily fortified strongpoints often connected by tunnels with ammunition and food stockpiles.
• Japanese response was to dig in and dig deep for defense.
• Assigned to Iwo Jima in June 1944, General Tadamichi Kuribayashi began extensive defensive preparations, working at night to avoid aerial attacks.
• Kuribayashi learned lessons from the fighting on Peleliu,.
• Kuribayashi discouraged banzai charges, prioritizing delaying and inflicting casualties on the enemy.
• Before the Fifth Fleet started bombarding Iwo Jima, all Japanese civilians had been evacuated.
• Kuribayashi aimed to make the U.S. assault as costly as possible, using Iwo Jima’s difficult terrain to aid the Japanese defense.

The Battle

• Iwo Jima is eight square miles, shaped like a pork chop with its widest part toward the northeast.
• Mount Suribachi, a dormant volcano, dominates the island’s narrow southwestern tip.
• Iwo Jima had two completed airfields and one under construction from the southwest to the northeast along its centerline.
• Kuribayashi divided the island into five defensive sectors with central reserve areas.
• U.S. planners designated landing beaches on the southern and northern shorelines between Suribachi and the island's wider part.
• Only the southern beaches (Green, Red, Yellow, Blue) were used for the assault.
• Bombing raids and naval bombardment occurred against Japanese facilities on Iwo Jima beginning in June 1944, intensifying before D-day.
• Air raids damaged fortifications, but Navy underwater demolition teams underestimated the extent of Japanese underground fortifications.
• V Amphibious Corps requested a concentrated shore bombardment for 10 days before landings.
• Due to ammunition supply issues, Task Force 52 provided only three days of fire support.
• Adverse weather restricted bombardment on February 16, the first day, and only 13 hours of effective bombardment occurred.
• Fifth Fleet conducted minesweeping around the island, focusing on approaches to landing beaches.
• Spruance detached Task Force 58 to strike strategic targets on Honshu to support the Iwo Jima landings.
• Marines were unhappy of the shortened naval gunfire support, prioritizing continuous close air support for ground forces.
• At H-hour (0900 on February 19), the first assault wave landed on assigned beach sectors, with the 5th Marine Division on the left and the 4th Marine Division on the right.
• The Japanese held fire until 1000, after the Marines' first wave landed.
• Volume and accuracy of artillery and mortars indicated bombing and naval bombardment was not greatly effective.
• Casualties occurred in all sectors, with Green, Red, and Blue beaches being the hardest hit.
• The beaches were unstable due to steep terraces of shifting black sand, volcanic cinders, and ash, which made digging difficult and bogged down vehicles.
• Men, amphibious tractors, tanks, and supplies piled up at the waterline.
• They were subjected to Japanese artillery, mortar, and machine-gun fire.
• The steep beach gradient caused a violent surf zone.
• The landings were completed successfully under a rolling naval gunfire barrage and close air support from Fifth Fleet’s escort carriers
• The Marines began moving off the beaches.
• The 5th Marine Division pushed to the northwestern shore to isolate Mount Suribachi in ninety minutes.
• The 4th Marine Division advanced more slowly toward airfields, with one directly in front of the Marines.
• The second airfield required a wheeling movement to the northeast, exposing the division to heavy Japanese fire.
• By the end of D-day, about 30,000 personnel had been landed on Iwo Jima.
• Weather conditions deteriorated quickly & well-coordinated Japanese resistance put pressure on marines.
• The Marines crossed the island at its narrow width, cutting off Mount Suribachi, but the planned phase line was not reached and casualties were high.
• The beachhead was concentrated in a triangular area roughly 4,000 yards long and 700 to 1,100 yards wide.
• D+1 saw the landing of the 3rd Marine Division, the corps reserve, which then occupied battle space between the two previously committed Marine divisions.
• The 5th Division’s 28th Marine Regiment began its assault of Mount Suribachi.
• Mount Suribachi was garrisoned by 2,000 Japanese troops, possessing defensive positions and tunnels, one of which was seven levels deep.
• Bolstered by reinforcements from 3rd Marine Division, other 5th Marine Division units, and the 4th Marine Division, U.S. forces advanced northwest and northeast.
• Navy destroyers, assigned to Marine units, provided direct gunfire support.
• Marine tanks, amphtracs, and artillery provided mobile firepower, although were targeted by Japanese guns
• Fifth Fleet aircraft provided close air support, dropping napalm.
• Small teams of Marines, sometimes individuals, with flame throwers, satchel charges, and hand grenades (“blow torches and corkscrews”) destroyed Japanese strongpoints.
• Companies lost up to 50% of their pre-assault strength, with only yards of ground gained.
• The amphibious landing area were subjected to a kamikaze attack during the night of February 21–22, resulting in high casualties.
• The escort carrier Bismarck Sea (CVE-95) was lost and fleet carrier Saratoga (CV-3) was badly damaged.
• Marines reached the summit of Mount Suribachi on February 23 after the initial landing.
• Hidden pockets of enemy still resisted on the mountain.
• Airfield No. 1 was captured after fighting, and the armored task force helped marines move north.
• The Japanese launched coordinated counterattacks, as opposed to the banzai charges marines were used to.
• Tanks were disabled by mines, suicide squads, or antitan guns.
• Marine rifle companies were targeted by artillery, mortar, and small-arms fire.
• Japanese positions proved impervious to close air support bombing and required direct ground assault or sealing off entrances.
• After nine days, the drive north had progressed 4,000 yards at a cost of 7,000 U.S. casualties.
• By March 4, Airfield No. 2 had been secured & General Kuribyashi’s defenses were degraded to the point at which many Japanese heavy weapons were out of action.
• On March 4, the 9th Bomb Group's B-29 “Dinah” made an emergency landing on Airfield No. 1, refueled, and departed.
• On March 14, the island’s occupation was officially announced, although fighting continued for two further weeks.
• On March 26, Iwo Jima was declared “secure.”

Aftermath

• Of the 21,000 Japanese defenders, 216 were taken prisoner & approximately 3,000 went into hiding after U.S. occupation of the island.
• By August 1945, one group did not surrender.
• General Kuribayashi committed suicide in his command post on March 23, 1945
• American operators determined the Japanese radar station could not provide early warning data to Japanese Home Island air defenses.
• Before Operation Detachment, the Japanese had written off the island’s airfield.
• Iwo Jima’s airfields presented a challenge.
• Utilizing Iwo Jima’s airfields for U.S. escort fighters proved logistically difficult.
• The P-51 pilots faced a 1,500 nautical mile round trip.
• The fields were limited, with the capacity of one Navy fleet carrier and few B-29.
• The airfields hosted search-and-rescue operations & aircraft picked up downed U.S. aviators
• Operation Detachment cost U.S. forces 6,871 killed and 19,217 wounded.
• 22 Marines and five Sailors received Medals of Honor, with 14 posthumously
• Admiral Chester W. Nimitz noted, “uncommon valor was a common virtue.”