This attack is an ok move, but it will limit some of the other things you could accomplish during your J1. You have pushed the US to max income and made his immediate objective clear (pushing you back off Hawaii). Considering that you have limited income in this scenario, his 70 should trump your 40, and he will eventually push you out of SZ 26. Because of this focus on the USA, other objectives (building factories, capturing VCs, money and india) may be missed, and so you would probably be less-well prepared to win the game or defeat america by trying to confront your biggest opponent first. What’s at risk is only 1CA 1 DD 1 SUB and 1 TT, so that reward has to be measured against the other things you could have done and like oystello says, its only a 6$ income swing. A easier way to approach this as japan is to spend your first 5 turns getting 5 VCs the old fashioned way, and then, while America is focused elsewhere or splitting his forces, take Hawaii (or Sydney) as the last VC with your plodding megafleet built over the course of the whole game and not diminished by the attrition you’ll suffer if you try to get into an early naval pawn for pawn type trade