Dec. 7, 1941, wasn’t the end of Japanese attacks in and around Hawaii.

Enemy submarines prowling around the U.S. territory and operating off the West Coast sunk ships and added to fears 75 years ago that a Japanese invasion was planned.

In fact, the seizure of Hawaii was envisioned by Adm. Isoroku Yamamoto, commander in chief of Japan’s Combined Fleet and architect of the Pearl Harbor attack, as a bargaining chip to force the United States to negotiate a truce, according to historian John J. Stephan.

One of the greatest losses of life for Hawaii after the Pearl Harbor attack came on Jan. 28, 1942, when the military transport ship Royal T. Frank was torpedoed and sunk 30 miles off Hawaii island’s Upolu Point.

Seventeen young Army draftees from Hawaii who had just completed basic training at Schofield Barracks perished along with 12 crew members. Nine Big Island men survived — later to be nicknamed the “Torpedo Gang.”

Japan arrayed as many as 25 submarines around Hawaii for the Dec. 7, 1941, attack to sink any ships that tried to escape Pearl Harbor. Part of that force remained after the aerial bombardment.

On Dec. 11, the freighter Lahaina, carrying molasses and scrap iron, was hit 800 miles from Hawaii. Three days later the Norwegian motorship Heough was sunk near Kauai, wrote Michael Slackman in “Target: Pearl Harbor.”

The Manini, a Matson freighter, was torpedoed near Hawaii. So was the freighter Prusa, 120 miles south of Hawaii.

Slackman said the Japanese submarines I-1, I-2 and I-3, with 4.7-inch deck guns, shelled Maui, Kauai and Big Island harbors in December 1941.

“The first attack occurred shortly before dark on Dec. 15,” Slackman wrote. “A surfaced submarine fired about 10 shots into the Kahului, Maui, harbor area. The only hits were on a pineapple cannery, where three rounds caused about $700 worth of damage.”

Nawiliwili, Kauai; Hilo; and Kahului were hit Dec. 30-31 in coordinated shellings — with the same ineffectiveness, according to Slackman.

After the Pearl Harbor attack, U.S. military leaders rushed to reinforce Oahu with men, munitions, planes and ships. Convoys brought about 15,000 more troops to Oahu, raising the Army’s Hawaiian Department strength to 58,500 personnel.

The Navy’s patrol bomber complement rose to just under 100 planes. The Navy also ordered the transfer of three battleships and an aircraft carrier from the Atlantic to the Pacific.

On Dec. 10, an SBD-2 Dauntless from the USS Enterprise spotted the Japanese submarine I-70 on the surface north of Hawaii and dropped its single bomb, apparently damaging the vessel. Another aircraft from the Enterprise also damaged the I-70, which finally went down after it was depth-charged by a destroyer.

Nine Japanese subs were ordered to attack shipping off the West Coast, arriving there in mid-December, while at least a dozen remained off Hawaii.

“On balance, the record of Japanese submarines in Hawaiian waters at the time of the air strike and for at least a month afterward was more one of missed opportunities than successes,” wrote Carl Boyd and Akihiko Yoshida in “The Japanese Submarine Force and World War II.”

Yamamoto, meanwhile, had ordered his staff on Dec. 9, 1941, to prepare plans for a land invasion of Hawaii, historian Stephan wrote in “Hawaii Under the Rising Sun.”

“By 1942 Yamamoto saw the seizure of Hawaii as a political as well as a military act, a stroke through which Japan could extricate herself, via a negotiated peace, from a war that would prove ruinous if it were not terminated quickly,” wrote Stephan, who taught modern Japanese history at the University of Hawaii.

The Battle of Midway, June 4-7, 1942, was intended by Japan to be a decisive victory over the U.S. Pacific Fleet, but, “Midway itself was but one step toward Hawaii,” Stephan said.

Capt. Shigenori Kami was ordered to analyze an invasion of Hawaii, completing the study on Jan. 11, 1942, and concluding that “Hawaii could be captured but supplying it would pose great difficulties because of a shortage of shipping,” according to Stephan.

The Army General Staff envisioned an invasion force of 45,000 soldiers for the “Eastern Operation” Hawaii invasion, he said.

The outcome of Midway changed that. Japan lost four of the aircraft carriers that took part in the Pearl Harbor attack, 332 of its best aircraft, and 3,057 men. Japan’s momentum had stalled and with it any plans for a Hawaii invasion.

“Could Hawaii have been successfully invaded during the Greater East Asia War? Yes, and it nearly was,” Stephan said. “Only the unexpected reverse at Midway aborted ‘Eastern Operation.’”