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 1.9 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-20, one of five that took part in the Japanese attack on Pearl Harbor on December 7, 1941. On the morning of the attack on Pearl Harbor, USS Ward, a Wickes-class destroyer, sighted HA-20’s periscope as it was following the American cargo ship Antares. Ward attacked HA-20 with its 4-inch guns and landed a hit at the base of the conning tower, sinking the submarine. This was the first American-caused casualty of the Pacific Theater during World War II.
The Hawaiʻi Undersea Research Laboratory rediscovered HA-20 on August 28, 2002. On December 7, 2016, NOAA Ocean Exploration and NOAA’s Office of National Marine Sanctuaries visited and explored HA-20 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 Insite Pacific Zeus Plus camera capable of collecting high-definition footage — was used to document the site, which is at a depth of approximately 400 meters.
This model of HA-20 is based on the ROV dive footage from timestamps 16:40 to 17:55. This footage was exported into 1,496 images using VLC Player. The footage collected during exploration of HA-20 was not intended for photogrammetry. While aligning the model, there was some distortion at the stern and misalignment on the port and starboard sides. individual port and starboard models were made and were then stitched together in Rhinoceros 8 and uploaded to Construkted Reality.
The full annotated video of this dive can be viewed on SeaTube.
Site Name: Japanese Miniature Submarine (HA-20)
Site Type: UCH
UCH Vessel Date Built: 1940
UCH Vessel Date Sank: December 7, 1941
Hull Material: Steel
Official Number: HA-20
Expedition Number: EX1608
Expedition Name: Shakedown, Calibration, and Testing in the Main Hawaiian Islands
ROV Dive Number: 05
ROV Dive Date: December 7, 2016
Location: South of Oahu, Hawai’i
Depth: 400 meters
Length: 23.9 meters
Width: 1.8 meters
ROV Used: Deep Discoverer
Camera Information: Insite Pacific 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: 1,496
Image Alignment Percentage: 85%
Number of Tie Points: 148,175
Link to Raw Images: https://www.ncei.noaa.gov/access/ocean-exploration/video/?cruiseId=EX1608&oerkey=DIVE05
Time to Complete: 4 hours
Orthomosaic Views Available: No
Images Available: Yes
Animations Available: Yes
Available File Exports/Location/POC: archaeology.oceanexploration@noaa.gov
Link to NOAA Ocean Exploration Project Page: https://oceanexplorer.noaa.gov/okeanos/explorations/ex1608_1609/welcome.html
Software: Agisoft Metashape Standard Version 2.0.1, Rhinoceros 8.
Developer: Raymond Phipps, NOAA Ocean Exploration explorer-in-training, July 10, 2023.
Credit: Model courtesy of NOAA Ocean Exploration, Shakedown, Calibration, and Testing in the Main Hawaiian Islands.
