I think I found a glitch - which helped me farm a lot of medals - it involves some clicking, but You have sure medal gain with each load. I work as a SW tester, so I tested this thoroughly and it really works (tried on multiple devices)
It appears, that the game generates some specific key after fresh loading - and its always the same = completely same attacks, completely same medal gains etc. This "key" (or how do You want to call it) - is somehow changed / re-generated with every re-start of your gaming device. But as long as You dont re-start Your device (total power off) - its same.
steps to do as preparation:
1 - play some scenario and prepare Your units into positions where they can attack many enemy units. It doesnt matter which scenario - but after all those hours spent with game - I had a feel that submarines give a bit more medals. Might be just a luck, no statistical data to prove it.
Anyway - i used scenario Operation Sealion from campaign - playing as german. On turn 4 I had 9 units available for attack from both land and sea. There was some infantry and tank on shore, some infantry on water and several ships and subs around left peninsula. All ready to attack, but no attacks done yet!
2 - save the game
3 - quit the game completely to android (or whatever system you have)
4 - open the game - load this saved game - attack with all units that can attack - try to remember the order in which the units attacked (i began with most western unit and continued to most eastern for example)
5 - try to remember (or write down) attack numbers and number of medals (for me - i got 3 medals, 1 by infantry, 1 by tank, 1 by submarine)
6 - quit the game completely
7 - repeat from step 4 .... You have 100% certainity of same attacks, same medal gains - Youll see and can thank me later
In case You are unlucky and dont get any medals at all in step 5:
restart your device completely
try step 4 again after restart - you will see, that this time, you have other attack numbers during step 5 and other medal gains
restart your device as many times as needed, until the generated "key" is enough for you and you can then farm as many medals in very short time.
My son restarted that device and i lost that great 3 medal gain session - so i restarted device several times and always tried my scenario. After 5th restart, I got to state where i always got 2 medals, so its good enough for me - as I upgraded most things I needed from previous farming.
hope it helps!
Nufajs