This is artwork by legendary manga artist Sanpei Shirato. The Google mechanical translation of this Japanese page appears to suggest that the art is related to the 2009 movie Kamui Gaiden, which was based on Shirato’s manga series (dating back to the 1960s) of the same name. The Wikipedia entry for the movie mentions “underwater battles” which perhaps helps confirm the connection.
Image provenance by Bacchus at Erosblog.