In the early morning hours of August 1, 1943, a total of 177 B-24 Liberator bombers took off from Allied airfields near Benghazi, Libya, heading northeast over the Mediterranean Sea with more than 1,700 U.S. airmen aboard. Operation Tidal Wave—one of the most daring, and costly, raids of World War II—had begun.

The target of the raid was the oil refineries near Ploesti, Romania, which provided about one-third of all the oil used by Nazi Germany and the other Axis powers. Dubbed “Hitler’s Gas Station,” Ploesti held great strategic importance for Allied leaders, who hoped its complete destruction would strike a lethal blow to the German war effort.

Up to that point, the Allies had largely relied on high-altitude precision bombing missions. But to attack the heavily defended Ploesti oil refineries, war planner Col. Jacob Smart came up with the idea of a surprise low-level attack that would help the advancing planes evade German radar.

At the time, B-24s were the only planes capable of flying the distance required for the mission, which totaled more than 2,000 miles round trip. Five B-24 groups from the U.S. Army Air Forces were involved in Operation Tidal Wave, including the 98th and 376th from the Ninth Air Force, and the 44th, 93rd and 389th from the Eighth Air Force.

“The key was that the fight group would follow each other into the target under radio silence, to not give the German batteries the chance to prepare for their arrival,” says Joe Duran, whose great-uncle, Joseph Avendano, flew in the Ploesti mission as part of the 93rd Bombardment Group.

Dubbed the “Traveling Circus,” the 93rd had already earned fame for its service in Operation Torch, the Anglo-American invasion of North Africa, and its exploits bombing Axis targets there and in Italy. In July 1943, a photo of its members had even appeared on the cover of Life magazine.

The Ploesti mission would prove to be the 93rd’s greatest test yet. Problems started immediately after takeoff, with the crash of one of the heavily loaded B-24s. A number of other planes aborted the mission, and only 167 remained as the groups flew over the Balkan Mountains, at an altitude of some 11,000 feet. When the planes began dropping lower, the groups became separated, with the lead groups (the 376th and 93rd) flying far ahead of the others.

To make matters worse, the lead pilot of the 376th took a wrong turn, leading the formation toward Bucharest rather than Ploesti. Several planes broke radio silence to communicate the error, and Lt. Col. Addison Baker of the 93rd was able to turn his group some 90 degrees and head toward the oil refineries.

The 93rd had planned to fly over Ploesti from the north, entering behind enemy fortifications. After the confusion, however, “they approached the target from the southern direction, which was where all the [German] batteries and the bulk of the large 88 [millimeter anti-aircraft guns] were placed,” Duran explains.

As Baker’s plane, Hell’s Wench, and the other aircraft of the 93rd approached the Ploesti refineries, they met an overwhelming barrage of 88-mm shells and other anti-aircraft fire. Hell’s Wench sustained heavy damage, but continued flying, with Baker and his crew jettisoning the plane’s bombs to stay in the air a little longer. The plane eventually crashed into a field, leaving no survivors. Baker and his co-pilot, Lt. John Jerstad, would posthumously receive Medals of Honor for their bravery, two of five that were awarded to U.S. airmen for the mission.

The other four bomb groups in the raid also braved heavy enemy fire as they attacked their targets, which included the oil field located further north, at Campina. In addition, the low-flying B-24s had to contend with explosions from below, as their bombs detonated on the oil refineries and set the massive gasoline tanks on fire.

“[The pilots] got down lower and lower, until they were flying over trees and actually just above the ground to get under the anti-aircraft,” Duran says. The surviving airmen “ended up with branches in their bomb bays, and barbed wire, which [means] they were flying almost on the ground.”

Of the original 177 Liberators that departed Benghazi for Operation Tidal Wave, only 92 returned. Germans destroyed 54 of the bombers, while others were able to land in other Allied airfields. More than 300 U.S. airmen were killed in the raid, with more than 100 captured by the Germans and nearly 80 interned in Turkey after their planes were forced to land there.

Despite the bravery on display on “Bloody Sunday,” as historians dubbed it, the Ploesti mission was a strategic failure. “Hitler’s Gas Station,” though damaged, was not destroyed; the oil refineries were back at full production within weeks. “It took many more missions, mostly done at a high altitude, to eventually knock out that oil field,” says Michael Sellers, a filmmaker whose late grandfather, John L. Sullivan, served as a bombardier navigator in the 93rd.

By war’s end, the “Traveling Circus” would fly 396 missions, more than any other bomb group in the Eighth Air Force. Members of the 93rd, along with later generations of their family members, have met for decades in reunions in the United States as well as at Hardwick, the former air base in England where the group made its home during the war. Sellers chronicles the ongoing reunions (the first one of which he attended with his grandfather in 2001) and the 93rd’s wartime service in his documentary Return to Hardwick: Home of the 93rd Bomb Group.

Avendano, Duran’s great-uncle, survived the Ploesti mission, but was killed during a test flight in England in January 1944. “It was not just to remember my uncle, but all the veterans that served in the Army Air Force, and specifically in the 93rd Bomb Group,” Duran says of his work researching Operation Tidal Wave, as well as his visits to Hardwick and other reunion activities. “It was our wish to keep their legacy alive.”