Suddenly they spotted an undamaged weir, moved quietly across the river and quickly established a bridgehead, unnoticed by French defenders nearby. The crossing that night 70 years ago Wednesday, the pivotal moment in one of the most important battles in modern history, gave rise to the doctrine of the "lightning war" - or Blitzkrieg - which many armies have since sought to emulate and even today holds relevance for campaigns in Afghanistan and elsewhere.
"Since 1940 the Blitzkrieg has been the benchmark of maneuver warfare," said Lloyd Clark, senior lecturer of war studies at Britain's Royal Military Academy at Sandhurst. "The Germans brought it to a pitch of excellence, and since then everyone's been trying to copy them."
The U.S. military used a battle plan directly inspired by the Blitzkrieg to sweep aside Saddam Hussein's demoralized army in Kuwait in 1990, and the Israelis used the same strategy to overwhelm Arab armies in the 1956 and 1967 wars.
But more recent conflicts have shown that this strategy - defined as the grouping of combined arms to focus overwhelming force against the enemy's front and to quickly exploit the ensuing breakthrough - is far from foolproof.
In 2002, the U.S. used "shock and awe" tactics to defeat Saddam's forces and occupy Iraq, a year after easily dismantling the Taliban regime in Afghanistan. But neither campaign achieved a knockout victory, and the wars gradually turned into slow, bloody slogs against outgunned but evasive insurgents.
Similarly, the Soviets mounted their own attempted Blitzkrieg in Afghanistan in 1979, quickly overrunning the country. But they then got stuck in a decade-long quagmire against religious fundamentalist insurgents.
When Israel tried lightning attacks against skilled Hezbollah fighters in southern Lebanon four years ago, they were defeated even though Hezbollah had fewer troops and lighter weaponry.
"They generally manage to get away with it when the enemy wasn't very good," Clark said. "But when they came up against stronger opponents, it proved difficult to achieve success."
(Left: German Field Marshal Gen. Erwin Rommel reviews the crew of a German coastal battery on the English Channel, in France, March 1944.)
By June, the stunning breakthrough had established the Nazi Third Reich as the master of Europe.
"(The Blitzkrieg) proved to work only in certain very specific circumstances," Clark said. "Even for the Germans, the wheels literally came off the Blitzkrieg in 1941 when they attacked the Soviet Union, a much more serious enemy."
Some prominent historians now even question whether the Blitzkrieg as a premeditated strategy ever existed, saying the term was concocted by Nazi propagandists after the campaign in order to convince potential enemies of the futility of resisting Germany's military might.
They point out that the German High Command had never envisioned a quick victory over their numerically superior opponents. Instead, it had prepared for a slow and steady offensive. The swift campaign was an unforeseen result of lucky circumstances, gross Allied incompetence and commitment to the fixed defenses of the Maginot Line, and the audacity of a handful of German panzer commanders, they say.
At the Houx crossing, for example, the weir and a catwalk across a canal lock had not been blown up because two French units defending the same sector could not coordinate who should carry out the demolition. A series of such jaw-dropping blunders throughout the campaign cleared the way for the German breakthrough.
German army historian Col. Karl-Heinz Frieser, author of "The Blitzkrieg Legend" (Naval Institute) has painstakingly debunked what he says are the myths associated with that stunning victory 70 years ago.
"The 1940 campaign had not been planned as a Blitzkrieg," he said. "The German High Command was planning a repeat of the long struggle of World War I (and) was completely surprised by the course of the operation."
"Propaganda pictured the Blitzkrieg as an invention of Hitler, 'the greatest warlord of all time,'" Frieser said.
But a panic-stricken Hitler had in reality sought to halt the lightning breakthrough fearing Allied counterattacks against the exposed flanks of the German spearhead, he said.
Ultimately, the propaganda claims proved disastrously counterproductive because they had the unintentional effect of persuading Hitler and his generals that they could easily crush any other enemy, Frieser said.
"The campaign in the West appeared to be an unexpectedly easy victory which led to the dangerous assessment that it would be possible to win easy victories everywhere," he said.
(Left: The frozen bodies of dead German soldiers lie sprawled across a roadside southwest from Stalingrad, on April 14, 1943.)
Other historians in the United States and Britain agree that the unusually rapid victory in 1940 was indeed unplanned. But they have pointed out that with commanders such as Rommel and Guderian, it was likely that the Germans would have triumphed even without the breakthroughs at Houx and just hours later at the French town of Sedan.
"When you have someone like them in charge of Panzer groups, and at a command level where they can control events on the ground, then unexpected things are going to happen," said Martin Windrow, a British historian and expert on France's armed forces.
By Associated Press Writer Slobodan Lekic