The Arpeggio missions are wrapping up now, since the partnership between the anime and WG ends as of January 2017. So, after waiting so long for new missions, NA is getting plenty of them at once; the final mission, for all servers, is expected to be for ARP Takao, is coming in November.
This month’s missions are for Nachi and Haguro, a pair of Myoko-class cruisers; the former’s missions can be done by T6+ ships, the latter’s T4-5. The missions last all of October.
They both require you to deal a total of 1,300,000 damage over three missions, but you’ll have to grind each separately due to the tier restrictions. Nachi won’t be so hard, but Haguro might prove to be annoying considering the same amount of damage needs to be done in ships that generally don’t have as much firepower as, say, T10 battleships. Good luck!