What were the advantages of submarines in ww1?

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Tags

1. #relied
2. #world
3. #germans
4. #economy
5. #choke
6. #strong
7. #supplies
8. #extremely
9. #important
10. #tactics
11. #submarines
12. #wanted
13. #those
14. #block
15. #submarine
16. #warfare
17. #enough
18. #surface
19. #against
20. #english