August 15, 1914
The 21-centimeter mortars and infantry continued to engage Liège’s remaining forts. Forts Boncelles and Lantin surrendered. The 42-centimeter mortars joined the 21-centimeter in the destruction of Fort Loncin. This was also Leman’s location. Restricted to the fort, it is questionable how much he actually influenced the defense after the Handstreich. At 1710 hours, the nineteenth 42-centimeter shell, with a delayed-action fuse, exploded in a magazine containing twelve metric tons of powder, creating a crater thirty meters in diameter and six meters deep. Fort Loncin surrendered, and with this the defense of Liège collapsed. The Army of the Marne was disbanded and FFA 9 assigned to Second Army. Ninth Corps was placed back under the orders of First Army, and the brigades of Third and Fourth Corps, which had been employed against Liège, rejoined their parent formations. First Army was now clear of the gap between Liège and the Dutch frontier, and the OHL gave First Army time to close up, expecting the two armies to be abreast shortly. Finally, the Germans could get going.
Once Fort Loncin became victim of the enormous power of the 42-centimeter mortars, the route to France lay open. There has been a lot of discussion about how much of a delay the battle of Liège cost the Germans. Many authors had different opinions; not all seem steeped in any kind of logic. If there was a thought that the Belgians would not oppose the Germans, then the general advance would have started days earlier, into a vacuumthat the cavalry and the Army of the Meuse could advance unopposed.
But the Belgians decided to defend Liège, making it an academic discussion at best. So how long did the Belgian defense of Liège delay the German Army? This question has an easy answer. Kluck reported, “August 13 was therefore fixed as the date for the march through Aix-la-Chapelle (Aachen) instead of the tenth.” So the OHL originally envisioned First Army would begin not finish vacating its assembly areas on August 10, taking five days to clear Aachen. That operation was delayed three days—the beginning of active operations as reported by Bergman was August 13.
Could First Army have moved on August 10? Yes. What created the delay was the Belgians and the “technical problems” caused by the defense of Liège. Somewhere between the interdiction of the forts and the destruction of the railroad tunnels, the OHL delayed First Army’s movement by three days. The GOH, however, indicated no real delay and asserted that the advance happened just in time. Stig Förster wrote in 1921 that the German deployment timetable had required its armies to reach Mons by the twenty-second day of mobilization (August 23, right on time).The British official history cited a later recollection of Kluck’s that gave the defense credit for four to five days. Bülow reported that the OHL had wanted to start movement on the August 10 but was forced to delay it until the seventeenth. Both Sewell Tyng and Strachen claimed a forty-eight-hour delay but focused on the inability of First Army to concentrate all its active forces until August 13. It had always been the plan of the OHL to bring the two armies abreast first and only then begin the general advance. First Army had the longest way to go and would require the most time. So, what becomes paramount is when First Army started to move, not when its last unit left the assembly area—and the OHL delayed the start three days.