All Zipang released episodes
The JDS Mirai sets sail from Japan as one of a four-ship squadron going to Hawaii to participate in a joint exercise with the United States Navy. In the vicinity of Midway Island they encounter a strange meteorological anomaly. The Mirai loses contact with her sister ships but finds herself sailing straight for what can only be the Imperial Japanese Navy battleship Yamato.
The Mirai finds itself in the middle of the Combined Fleet formation of the night before the Battle of Midway. First, Mirai is signaled by the Yamato, the Combined Fleet flagship, then two destroyers attempt to block its path, but it successfully eludes the Imperial Japanese fleet using superior acceleration from modern gas turbine propulsion. Reluctantly, the crew realizes that they have traveled sixty years into their past, to the eve of the Battle of Midway. They witness the battle but make the difficult decision to not become involved so as not to affect history. Captain Umezu decides that, since they obviously cannot enter Pearl Harbor to reprovision as originally planned, they should head back to Yokosuka and hope that they may encounter the anomaly again on the return trip.
Kadomatsu rescues an Imperial Japanese Navy officer, Lt. Commander Kusaka, from a sinking seaplane. The Mirai’s crew is split over the fact that they may have changed history. The Mirai is discovered by an American submarine, USS Guardfish (SS-217).
The Mirai narrowly escapes the American sub’s torpedoes. A panicked sailor in the CIC launches an ASROC. Captain Umezu considers sinking the sub but, at the last moment, self-destructs the ASROC. The Americans escape with knowledge of a new Japanese ship with incredible capabilities. Kusaka learns that the ship is from the future. On board the battleship Yamato, Admiral Yamamoto summons Lt. Tsuda, a naval intelligence officer, to investigate the strange warship flying hinomaru that mysteriously appeared and quickly disappeared in the midst of the Combined Fleet just before the Battle of Midway.
Kusaka is given access to the Mirai’s record room and learns the outcome of the war and the future of Japan. He decides to throw in his lot with the Mirai. He is shown quoting from a speech by Sun Yat Sen in Kobe on November 28, 1924, when Sun asked whether Japan will seek Western way of domination (覇道) or Eastern way of kings (王道) as its future policy, as he weeps over the future that would descend on Japan. The VTOL Umidori is sent on a recon mission over the Japanese naval base at Chichi-jima in the Ogasawara Islands to evaluate the situation before sailing towards Honshu. While daydreaming about his grandfather, who is from the island, the overconfident pilot is engaged by two Japanese floatplane fighters whose pilots think it suspicious that the odd-looking plane should be trying to escape, despite the presence of the hinomaru insignia.
The VTOL recon plane damages the two fighters and forces them to ditch without injuring their pilots, but its weapon systems officer is killed, the Mirai’s first casualty. Kusaka proposes that the Mirai go to Japanese-occupied Singapore, rather than Japanese mainland, to refuel and reprovision, He believes that he can arrange the resupply, armed with forged documents and fake currency produced on board the ship. Having examined Japanese Navy's personnel records in Mirai's record room extensively, Kusaka is certain that there is no one in Singapore who would recognize him.
Kadomatsu and Kusaka travel by the Malayan Railway to Singapore, while the Mirai hides in the Anambas Archipelago. Kadomatsu gets a view of the colonized people and has a close call with a brutal Kempeitai inspection. In Singapore, Kusaka requisitions a tanker to carry supplies for a "special mission" for the navy. While waiting for the ship to sail, Kadomatsu and Kusaka attend a party. There, Kusaka is shocked to run into Lt. Tsuda, his kohai from the naval academy, who, according to Mirai's records, should not have been anywhere near Singapore. He remarks to Kadomatsu that this is no longer his past, since the actual events are already diverging from the records of Mirai's past — as evidenced by Tsuda's unexpected appearance in Singapore. Kadomatsu refuses to believe this and punches Kusaka in the face. In the meantime, the Mirai is spotted by a local fisherman.
The two from the Mirai arrange for a tanker loaded with fuel and provisions to rendezvous with the destroyer. But Lt. Tsuda, having recognized Kusaka and realizing something odd is afoot, has found out about the ship. After being informed of the fisherman's discovery of a hidden Japanese warship in Anambas, he realizes that his encounter with Kusaka, mysterious purchases of fuel and foodstuffs on the black market, the unexplained "special mission" involving the tanker, and his mission regarding the mystery ship are all connected. He has the tanker’s crew replaced with his own men and confronts Kusaka after the ship sets sail.
Tsuda reveals that, in addition to the crew of the tanker, he has put together a sizable task force at Singapore around the cruiser Kashii for dealing with the mystery ship that he has been ordered to investigate, should it become necessary. However, Kusaka and Kadomatsu convince Tsuda that force will not work and ensure that the Mirai is fueled and provisioned accordingly. Tsuda has an opportunity to tour the Mirai but has difficulty coping with knowledge of the future. Kusaka tells Tsuda that the future is not fixed as recorded in Mirai's history, since its very presence is actively forcing changes, and that their job is to ensure that these lead to a "better" future for Japan. Specifically, he informs Tsuda that he intends to convince Captain Umezu and Admiral Yamamoto to change the outcome of the Battle of Guadalcanal. Captain Umezu accepts Kusaka's suggestion, though with much difficulty, and calls for a meeting of the senior officers to plan their moves.
Lt. Commander Oguri and Lt. Satake visit the crew of the tanker and the sailors from the 21st and 20th centuries have an opportunity to learn about each other — and Oguri consequently arrives late and drunk to the staff meeting called by Captain Umezu. Plans for Guadalcanal are developed. Kikuchi thinks the Mirai should intercept the U.S. fleet and inflict enough casualties to convince the latter not to press the attack but Kusaka argues that Americans would not give up so easily and instead proposes to fly to the Japanese base at Truk to convince Admiral Yamamoto to withdraw Japanese forces instead so as to avoid the battle.
Made this as general as possible in order to be spoiler free. If you enjoy history or militaria in general then this will suit you pretty well. Rather than a dick waving power fantasy it is the exact opposite, each encounter is a dangerous situation which the JMSDF tries to defuse as peacefully as possible, even against the IJN. The characters react in very human ways to the events unfolding around them, the hardware is spot on whilst the plot makes you want more and more. Unfortunately it ends with a bit of a cliff hanger, the manga has continued far past where the anime ends so if you want closure that is your best bet. The only unrealistic thing I could think of would be the strange VTOL which does not exist IRL. Great movie, excellent writing and the combat scenes were as authentic as you can expect from an anime, in fact more than I expected.