The bulletproof vest shown is a WWII United States Army Air Corps flak jacket developed for air crews' protection from anti-aircraft shell fragments.
Hogan mentions the Johnstown Flood. In 1889 a dam collapsed and Johnstown, Pa was instantly washed off of the map. Over 2,200 people died in a few minutes. However, Hogan probably meant the 1936 Johnstown, Pa. flood, aka the St. Patrick's Day Flood. Heavy rains caused widespread flooding that killed 24 people and did tens of millions of dollars of damage. This finally pushed Congress to pass the Flood Control Acts of 1936 and 1937.
Maurice wants to return to Vichy France. While the Nazis did not occupy the south eastern (Vichy) part of France and the Vichy had sort of a surviving French government, it was a puppet government. This 'Free Zone' was a collaborationist regime and a client state of the Nazis. The two million French POWs held in Nazi camps guaranteed the Vichy did not act against the Germans.
The sequence where Hogan, LeBeau, and Newkirk go out to retrieve the bulletproof vests - from exiting the tunnel to actually opening the dropped box, is re-used again in Is There a Doctor in the House? (1968).
When the case of bulletproof vests is ejected from the plane, the stock footage initially shows a man jumping from the plane. Cut to Hogan and the men, then back to what is now a large case and a parachute.