A gunkan is a kind of sushi also known as "battleship sushi" in Japan.
The reason gunkan sushi is called battleship sushi is because of the sushi's unique shape.
Gunkan or battleship sushi is made of a small oval of sushi rice that is wrapped in a strip of nori seaweed to form a vessel for soft or even finely chopped toppings.
Common soft or finely chopped toppings for gunkan sushi are salmon roe "ikura", sea urchin "uni" or even seafood salads.
And the nori lined rice balls also hold the delicate ingredients in place, which also prevents them from falling off.
The name "gunkan" also comes from it's resemblance to a battleship.
A strip of nori seaweed is wrapped around a hand formed oval of sushi rice to create a container.
And it's designed to hold toppings, which are difficult to use on traditional nigiri, like ikura or salmon roe, sea urchin also known as uni as well as various spicy or even mixed seafood salads.
The gunkan sushi style was also invented in the early 20th century at the Kyubei restaurant in Tokyo to accommodate other soft toppings.
Gunkan sushi is also meant to be eaten in a single bite, which allows the flavors to meld together.