4 ideas
Travellers in the Indian Ocean are shipwrecked after pirates attack their ship, and they wash up on a remote island. There they find Captain Sakuragi, a Japanese naval officer who, with a band of loyal volunteers, has secretly built the Denkōtei, a ram-armed submarine warship. The vessel strikes from beneath and sinks pirate craft, and its builders mean to offer it to Japan as a weapon in a future war against Western powers.
The decisive national weapon is built in secret, outside official channels, by self-funded loyalists who act before their government knows it needs the weapon. Their loyalty takes the form of unilateral initiative. The individual anticipates the nation's future war and prepares for it privately, then presents the result as a gift.
A technologically late nation cannot match established powers ship for ship. It can overturn the balance with a single breakthrough weapon that the incumbents have not imagined. Secrecy and novelty count for more than scale, so invention becomes the latecomer's path to parity.
Choosing pirates as the enemy lets a rising navy show its strength while casting itself as a policing, order-restoring force rather than an aggressor. The lawless adversary makes armed expansion into distant waters look defensive and righteous. It also serves as a dress rehearsal for conflict with real rival states.