The Japanese Type A kō-hyōteki miniature (mini or midget) submarines were built from 1940 to 1943 in Japan. These mini submarines had an overall length of 23.9 meters, a beam of 1.8 meters, a displacement of 46 tons submerged, and a test depth of 30 meters. They were equipped with two 450 millimeter torpedoes loaded into two tubes on the bow and one 140 kilogram scuttling charge. 

This particular mini submarine was identified as HA-16, one of five that took part in the Japanese attack on Pearl Harbor on December 7, 1941, and one of two believed to have entered Pearl Harbor and fired their torpedoes at battleship row. In 1951, the U.S. Navy located the submarine believed to be HA-16 in shallow water off the entrance to Pearl Harbor. It had been damaged from a scuttling charge. It was then raised, taken out to sea, and dumped in deep water. 

The Hawaiʻi Undersea Research Laboratory rediscovered three pieces of the HA-16  mini submarine south of Pearl Harbor during submersible dives in 1992, 2000, and 2001 (the stern section, midsection, and bow, respectively). On December 7, 2016, NOAA Ocean Exploration and NOAA’s Office of National Marine Sanctuaries explored HA-16 on the 75th anniversary of the attack on Pearl Harbor during a shakedown expedition aboard NOAA Ship Okeanos Explorer. Remotely operated vehicle (ROV) Deep Discoverer — equipped with an Insight Pacific Zeus Plus camera capable of collecting high-definition footage — was used to document the site, which is at a depth of approximately 500 meters.

The footage used for the three photogrammetric models of the HA-16 site was from timestamps 21:20 to 22:00 for the midship section, 22:15 to 22:50 for the stern section, and 23:15 to 23:55 for the bow section. This footage was processed into still images using Photoshop and was not color corrected. 2,321 images were used for the three photo models of the site. The footage collected during exploration of HA-16 was not intended for photogrammetry. While aligning the models, there was some distortion at the break point on the stern and bow sections that caused the port and starboard sides to misalign. To address this, three individual models were made. 

The full annotated video of this dive can be viewed on SeaTube.

Site Name: Japanese Miniature Submarine (HA-16)

Type: UCH

UCH Vessel Date Built: 1940

UCH Vessel Date Sank: December 7, 1941

Hull Material: Steel

Official Number: HA-16

Expedition Number: EX1608

Expedition Name: Shakedown, Calibration, and Testing in the Main Hawaiian Islands

ROV Dive Number: 06

ROV Dive Date: December 7, 2016

Location: South of Oahu, Hawai‘i

Depth: 500 meters

Length: 23.9 meters

Width: 1.8 meters

ROV Used: Deep Discoverer

Camera Information: Insight Zeus Plus HD, 3-CCD color camera with 2/3-inch 2,200,000 pixel 1080i IT CCDs

Video or Stills: Video

Number of Images Used/Format: 2,321/JPG

Image Alignment Percentage: 92%

Number of Tie Points: 365,067

Link to Raw Video Footage:

Time to Complete: 4 hours

Orthomosaic Views Available: No

Images Available: Yes

Animations Available: Yes

Available File Exports/Location/POC:

Link to NOAA Ocean Exploration Project Page: n/a

Software: Agisoft Metashape Standard Version 2.0.1.

Developer: Raymond Phipps, NOAA Ocean Exploration explorer-in-training, July 6, 2023.

Credit: Model courtesy of NOAA Ocean Exploration, Shakedown, Calibration, and Testing in the Main Hawaiian Islands.