France

On July 19, Company A began work on another critical project, Job No. 502, extending a line south from Lison toward Marigny —a town still firmly in German hands. This assignment would prove particularly dangerous, as they were essentially stringing communications wire toward active enemy positions.

Work continued under increasingly dangerous conditions until July 23, when German artillery found their range. Enemy shells exploded near the work site as the open wire pushed toward Marigny, injuring five linemen—one seriously. The sobering reality forced commanders to halt the job until advancing infantry could push the German guns back to a safer distance.

This work occurred in parallel with the larger St. Lô offensive (the "St. Lô breakthrough"), which broke the German defensive line and set the stage for the breakout into Brittany and central France. The 40th's efforts at Marigny directly supported communications during this pivotal push.

Meanwhile, Company B faced a complex engineering challenge at the Carentan Canal. They initially replaced existing cable with submarine cable laid underwater to allow clearance for water traffic.

However, as the massive Landing Ship Tanks (LSTs) bringing supplies ashore required even more clearance, they ultimately had to replace the submarine cable with open wire telecommunications lines strung on tall poles high above the canal. This demanding work required splicing poles together and pulling heavy copper wires over and across the waterway while maintaining signal quality throughout the operation. The job was completed on July 25.

The First United States Army advanced southwest toward Marigny and Coutances. Three days later, Company B joined Company A on Job 502.

On July 29, survey teams from Company B achieved an unexpected milestone when they captured four German prisoners near Marigny—the battalion's first enemy captives. For a communications unit, taking prisoners was an unusual but welcome departure from their primary mission of stringing wire, demonstrating that these signal soldiers were ready for whatever the war demanded of them.

Headquarters and Company B moved to new positions near Saint-Jean-de-Daye on 28 July, then toward Carantilly as the advance continued. The Battalion's last job for First Army was linking the new headquarters at Canisy to the VII Corps.

On August 1, the Twelfth United States Army Group under Lieutenant General Omar Bradley became operational, with First Army positioned on the left and Third Army on the right.

This major reorganization directly affected the 40th, which was reassigned from First Army to Twelfth Army Group command. The change reflected their proven capabilities and the critical importance of reliable communications for coordinating the rapidly expanding front.

This transition coincided exactly with Bradley assuming command of 12th Army Group on 1 August, formalizing Eisenhower's July 25 order and cementing the battalion's role in supporting the top-level headquarters of the American drive across France.

Major Tilton D. McNeal, the battalion's commanding officer, was promoted to lieutenant colonel in recognition of his leadership during these challenging operations.

The first task under Twelfth Army Group was building a line between Canisy and Saint-Sauveur-de-Landelin. The 40th built half of the line, meeting the 459th Battalion west of Marigny. This was completed on 4 August. This job connected front lines with Chateau des Mares Saint Sauveur Lendelin, a temporary command HQ for the Allied Forces.

A few days later, heavy German bombing near Pontaubault damaged communications wire and strafed convoys, though without casualties to the battalion.

This attack was part of Operation Lüttich ,Hitler's desperate counteroffensive at Mortain launched on August 7. The Führer had personally ordered this last-ditch assault to cut Allied supply lines by recapturing Avranches and severing the vital Pontaubault bridge over the Sélune River, through which seven divisions of Patton's Third Army had poured into Brittany in just three days.

The 40th's ability to maintain communications during this critical battle proved vital to the Allied response that ultimately destroyed over half the German tanks committed to the attack and sealed the fate of German forces in Normandy. Their wire lines at Avranches helped hold open the "Avranches corridor — the lifeline through which the entire Third Army continued its advance.

On August 7, the Battalion moved south to Bouceel, near Saint-James, and began construction of an eleven-mile communications line from Avranches to Saint-James. This route proved absolutely critical to Allied operations—it supported communications through the narrow Avranches corridor, the vital bottleneck through which seven divisions of Patton's Third Army had poured into Brittany in just three days. German forces were desperately trying to cut this corridor during Operation Lüttich, making the 40th's work a race against time.

By August 11, they had completed the essential line, ensuring uninterrupted command and control for the breakout operations. Meanwhile, Third Army advanced south and west, cutting off the Brest Peninsula. On 13 August, the Battalion moved to Clermont, setting up headquarters near the ruins of St. Bernard's Monastery (L'Abbaye de Clermont).

On 14 August, Company A laid cable from Saint-Ouën-des-Toits to Third Army Headquarters. The Battalion moved again the next day toward Le Mans. They bivouacked near Argentré, completing another line between 16 and 19 August.

On 24 August, the Battalion advanced 125 miles east to woods near Chartres. With the situation changing quickly, radio was for a time the main means of communication. The 40th connected Twelfth Army Group radio stations with Third Army at Pithiviers.

Paris was liberated on August 25, a moment of triumph that marked the symbolic heart of the liberation of France. Within days, the 40th found themselves positioned to support communications in the newly freed capital region. They moved to Ablis on August 27, then to Bois d'Arcy near the historic palace of Versailles on August 29.

From this location steeped in French history, they constructed a new communications line southeast of Paris, connecting Versailles to La Ferté and completing it on September 6. The battalion had helped provide the communications backbone for one of the most significant advances in military history—from the Normandy beaches to the liberation of the City of Light in less than three months.

At the very same time, 12th Army Group Headquarters itself was setting up in Versailles (Camp de Satory), meaning that the 40th's work directly supported Bradley's headquarters during its crucial early weeks on French soil.

Paris in particular became a bottleneck for the rail network. The 40th's positioning at Chartres, Ablis, and Versailles placed them at the heart of these logistical challenges, providing essential links in the overstretched communications web.

The broader context was that, between late August and late September, First and Third Armies swept across France to the Moselle and Siegfried Line, but supply lines were badly strained.