Jericho is a trio of agents working with Allied Intelligence.
They were formed to conduct operations usually behind enemy lines during World War II. Their area of expertise was the European continent and they covered a good deal of that region with their missions although much of their activity lay in France and Germany. Exactly how long they had been together is not known but all three are definitely experienced and skilled at their craft.
American Army Captain Franklin Shepphard, the leader of the trio, is an expert in psychological warfare. He is also an expert in planning operations and is the main designer of their activities. Likely in his mid to late 30's, Shepphard, the oldest of the three, was a Carnegie schooled civil engineer before the War and is "an expert in explosives and demolition"
British Royal Navy Lieutenant Nicholas Gage is brought in for his considerable knowledge of "getting in and out of deadly situations", especially useful when entry into secure locations is so difficult. He will routinely call upon his expertise gained by years in the circus before the War as a high-wire artist.
Free French Air Force Lt. Jean-Gaston André is highly skilled with weapons, "ancient and modern, large and small, their construction and use". While he is exceptionally good with handguns, his knowledge of arcane weaponry comes in handy on more than one occasion, such as when a catapult is hastily constructed and put to good use. He is the youngest of the three though only by a few years.
Also helping out on occasion, although not an official member of the team, is highly skilled undercover contact named Mallory who proves extremely valuable in providing local intel.