Hello Freddy

Wow! Thank you very much for the explanation, but I'm maybe a little slow today. Let me try the question another way:

The period that concerns me is January to July 1917. What happened before or after is, of course, interesting, but won't solve my puzzles.

Let's pretend that a German u-boat, an English destroyer and a French patrol boat met off Calais for tea on, say, 1 June 1917. They all recorded the meeting accurately in their logs.

The u-boat said the meeting happened at 1600 (the correct time for afternoon tea).

Question 1: What would the German-logged time of 1600 be relative to GMT?

Question 2: What time would the English destroyer log?

Question 3: What time would the French patrol boat log?

Question 4: Would any of these logged times above be different from that actual time at their bases? For instance:

4a: In Dover, where British summer time (GMT +1) was introduced in 1916 for 21/5-1/10?

4b: In Bruges, the U-boat's base?

4C: In Calais, the French patrol boat's base?

Question 5: Would any of these logged times change for any of the boats or any of their bases at any time between 1 January and 31 July 1917?

Thank you for holding my hand.

Chris Heal