https://sputniknews.com/military/201702281051117302-sweden-submarine-port/
http://www.upi.com/Defense-News/2017/02/23/Russia-to-lay-down-two-submarines-in-2017/4071487873846/
http://www.avclub.com/article/think-u-boat-was-beginning-submarine-warfare-think-250497
http://nationalinterest.org/blog/the-buzz/the-age-the-submarine-over-19474
https://sputniknews.com/videoclub/201702111050577998-nazi-submarine-descovery/
http://www.businessinsider.com/us-submarines-smaller-aircraft-carriers-2017-2