There are two types of activation method, Steam and Regular account. 

1) For Regular Account who are NOT Steam account

Go to https://forum.navyfield.com/plugin.php?id=nf2_users:activateid&lang=en

2)For Steam users, you will need 2 steps to activate your account:

a) Go to https://forum.navyfield.com/member.php?mod=logging&action=login&referer=&lang=en  to login to your Steam account by pressing the Steam login box

You will be redirected to Steam login page, login your Steam account

b)Then click Steam Step 2 or https://forum.navyfield.com/plugin.php?id=nf2_users:activateid&lang=en to enter the following info

Now you are ready for the sinking enemies! 

NavyField: Fleet Mission Management Team