"The Trouble With The Elsa Matter"
Published in The Victor #288, August 27, 1966.
Needing to get to a ride to Calais for his next mission, Captain Webb decides to make use of the German cargo vessel, the Elsa. Of course, being discovered on an enemy ship would not be a good thing.
[Note: this one-issue story probably should have come before the previous one. I could have my info wrong.]