[2] Major Seitz was in command of an infantry battalion at Schofield Barracks on the island of Oahu, Hawaii on December 7, 1941, when forces of the Empire of Japan launched their surprise attack on the United States naval base at Pearl Harbor and nearby U.S. military installations.

[17][18] Seitz and his battalion commanders occasionally had to face a slack attitude from a few veterans of the North Africa and Sicily campaigns who appeared to believe that they deserved to relax or were already adequately trained for combat.

[29] On June 7, the 1st Battalion, 26th Infantry Regiment, while still attached to CT 16, moved south to Russy and east to the important vantage point of Mount Cauvin, where they met up with British commandos.

[36] On June 9, 1944, Lieutenant General Gerow ordered the 1st, 2nd and 29th Infantry Divisions to continue to attack to the south, which led to the difficult and bloody fighting in the hedgerows of the Bocage.

[43] Patrols into the Bocage and shelling by German artillery strained the troops and inflicted a small stream of casualties while the 1st Infantry Division held their line.

[40][44] Efforts to move forward by the other divisions of the 1st U.S. Army also stalled in the Bocage, so the Allied penetration into Normandy was still shallow a month after the initial push off the beaches.

[45] Pursuant to that new plan, on July 13, 1944, the 1st Infantry Division was ordered to move 50 kilometres (31 mi) to the northwest of Caumont and assemble near Colombières.

[46] During CT 26's brief stay at Colombières, Colonel Seitz and his staff attended the funeral of the regiment's World War I commander, Brigadier General Theodore "Teddy" Roosevelt, Jr.[46] On July 19–20, the 1st Infantry Division moved to a location near Sainte-Jean-de-Daye, about 5 kilometres (3.1 mi) north of the line of departure for Operation Cobra, the Allied forces breakout from Normandy.

[49] By late afternoon, the VII Corps assault force had made sufficient progress so Lieutenant General Collins ordered the 1st Infantry Division to follow up the advance by moving south toward St. Gilles and Marigny.

[18] CT 26 drove the farthest south of any 1st U.S. Army unit and on August 8–9 turned northwest at Mayenne as part of the effort to encircle the Germans still in the Argentan-Falaise pocket.

[55][56] While the 1st Infantry Division held the ground south of the pocket, for the next eight days other Allied troops attempted to complete the encirclement of the Germans between Falaise and Argentan, with only partial success.

[57] On August 24, 1944, the 1st Infantry Division participated in the fast pursuit of the fleeing Germans for 170 miles (270 km) to the east to Corbeil, on the Seine River.

[63][65] On September 12, 1944, two battalions of CT 16 moved against bunkers 6 miles (9.7 km) southeast of Aachen, ran into heavy resistance and had to call for reinforcements.

[65][66] During the rest of September, the other battalions of CT 26 consolidated positions and tested German defenses near the southern edge of Aachen with help from the 33rd Field Artillery's counterbattery fire.

[77][80] On October 8, VII Corps commander Lieutenant General Collins sent more troops to the 1st Infantry Division and a force from the 9th U.S. Army to seal off the west side of Aachen in order to prevent the defenders from escaping.

[84] On October 10, Major General Huebner ordered Seitz to send two officers into Aachen with an ultimatum requiring the Germans to surrender unconditionally within 24 hours or to face artillery fire that would destroy the city and remaining resistance.

[73] To reduce the length of his front line before the assault on the city, Seitz moved a provisional company to face Aachen from the southwest and to tie in with the 1106th Engineer group.

[85] Seitz then had the mission of capturing the first German city to fall to the Allies in World War II, the ancient capital of the first Holy Roman Emperor, Charlemagne.

[97] For eight days, CT 26 cleared stubborn resistance across the city of Aachen, which required every building and cellar to be searched and enemy troops killed or captured.

[99] The Germans stiffly resisted CT 26's attack against the center of the city, Farwick Park and its buildings, and even briefly recaptured some ground in fierce counterattacks.

[107][notes 17] Seitz commented that CT 26 succeeded in capturing Aachen by employing "common sense, normal tactical principles, and maximum firepower.

[111] The corps had the mission of capturing the Roer River crossings by attacking northeast through the Hürtgen Forest between Jülich and Düren, a most difficult route over unfavorable terrain on which to advance.

[138] He found that CT 26 was separated from other U.S. Army units and would need to defend about 4 miles (6.4 km) of line with help only from the artillery and the benefit of a lake and a few streams that provided some flank defense.

[145] On December 23 and 24, 1944, 602 replacement soldiers brought the 26th Infantry Regiment, which had sustained casualties of about 25 per cent, up to 2,950 officers and men, close to a full complement.

Moreover, the strength of the fortifications on CT 26's main line of resistance, and the fortitude of its riflemen and machine gunners in manning firing ports after getting overrun by tanks, were also decisive in the battle's outcome.

[150] On January 24, 1945, in bitter cold and snow, the 1st Battalion, 26th Infantry Regiment captured Morscheck crossroads between Moderscheid and Büllingen, enabling the division to swing to the east.

[154] Seitz then spent 36 hours preparing for another attack which was to be supported by heavy artillery, flamethrowers and engineers with demolition charges and bangalore torpedoes to be used against pillboxes.

[2] As the war in Europe neared its close, the 69th Infantry Division met the Soviet Union's 5th Guards Army at the Elbe River in Germany on April 25, 1945.

[2] After World War II, Seitz was a student at the first post-war long course at the United States Army Command and General Staff College at Fort Leavenworth, Kansas.

[3] Seitz performed this duty during a tense period following the armistice when both vigilance and intensive training of the Republic of Korea Army was required.