At 2,200 yards (2,000 m), the extreme phosphorescence of the water illuminated her wake and betrayed her presence to the enemy ship, which began signaling the unidentified intruder with a blinker light.

After the tanker successfully evaded Tunny's third salvo, the submarine fired a last torpedo from 1,600 yards (1,500 m) as the intended victim reached the passage into Hong Kong.

Numerous junks plying the Formosa and Swatow banks at all hours added to the hazards imposed by shallow water, and an inoperable fathometer (depthmeter) made it impossible for Tunny to approach the shore closer than six miles (10 km).

Tunny launched three torpedoes from 960 yards (880 m) and noted a hit in the forward hold of the Japanese cargo ship before diving to 300 feet (90 m) to avoid the attention of the destroyer.

Some 15 minutes later, as Tunny started up to take a look, she was jolted by a deep-set depth charge which caught her at 260 feet (79 m), but caused only minor damage—a small price to pay for the sinking of Toyo Maru Number 2.

She then launched two torpedoes at the Kosei Maru, an 8000-ton passenger-cargo ship, scoring a hit amidships and one aft, and dove immediately to escape the inevitable wrath of the escorting Akatsuki-class destroyer which had been patrolling just ahead of the now-stricken transport.

Tunny quickly dove to 40 feet (12 m), turned right, ninety degrees, and launched four torpedoes from her stern tubes at one of the auxiliary carriers from a distance of 880 yards (800 m).

While approaching North Pass about 25 nautical miles (46 km; 29 mi) from Truk on 11 April, Tunny dove when a searchlight suddenly broke the night, 500 yards (500 m) ahead on the starboard bow.

An enemy plane added bombs to Tunny's immediate concerns, but she rigged for silent running and weathered the attack by remaining submerged until after nightfall.

Tunny dove to 44 feet (13 m) and began to swing for a stern shot when the belligerent destroyer increased speed to a thundering 30 knots (56 km/h) and headed in from a distance of less than 1,400 yards (1,300 m).

Silent running and a quick reversal of course eventually shook off the menacing destroyer, and Tunny returned to the surface after the moon set, noting only minor damage from the attack.

An unsatisfactory makeshift repair of the broken bridge speaker prompted a note in the war patrol report that "the only dependable communication system was the open hatch and a powerful set of lungs."

On 14 June, as Tunny cruised on the surface following a submerged patrol east of Murilo Island in the Hall group, one of her lookouts sighted a convoy bearing 090 degrees.

As Tunny made her approach, an unobserved escort vessel suddenly challenged her with a searchlight and several rounds of four-inch (102 mm) fire which fell astern.

On 26 June, she conducted routine and photographic reconnaissance of Saipan Harbor and Tinian Channel and, later that day, surfaced to patrol the Truk-Empire shipping lanes east of Rota Island.

Patrolling off Harnum Point and Rota harbor on 28 June, Tunny sighted a converted gunboat zigzagging madly, went to battle stations, and dispatched the enemy vessel with a salvo of three torpedoes from 1,500 yards (1,400 m).

Those on board felt the concussion of three sharp explosions close aboard, perhaps from aerial bombs, as Tunny went deep and rigged for silent running, maneuvering to avoid the trawler.

At noon, Tunny came to periscope depth and, finding no sign of the convoy, set her course for Toagel Mlungui, securing from battle stations after an exhausting 15 hours.

The explosions had jammed the gyro spindles in the stern torpedo tubes, impaired the usefulness of sound and radar gear, and caused other damage visible throughout the ship.

On 20 March, a persistent observation plane kept Tunny down for three hours off the entrance to Toagel Mlungui and dropped eight light bombs without damaging the submarine.

Tunny now obtained a setup on a destroyer moving at high speed across her stern, fired four Mark 18 torpedoes, then dove quickly even as depth charges from a nearby trawler exploded on the port quarter.

Apparently, the enemy had somehow received word of the Fifth Fleet's impending bombing attack on Japanese installations in the Caroline Islands and made a desperate attempt to clear the area.

Late in the afternoon, a larger formation appeared: the 63,000-ton battleship Musashi, the light cruiser Ōyodo, and three destroyers, also fleeing the expected aerial bombardment.

Incredulous watchers on the submarine saw the bomb cross over the deck gun on the bow, pass the bridge at what appeared to be no more than arm's length, and strike the water with a tremendous impact, only 10 yards (9 m) to starboard of the forward engine room.

[6] The entire ship lifted with a snap as if it had collided with an underwater object, and an explosion followed some seconds later, throwing personnel and gear in all directions in the maneuvering and after torpedo rooms.

Although the escorting vessels dropped 81 depth charges, none fell close, and Tunny withdrew to the southeast, having scored her sixth kill of the war, a 4900-ton cargo ship, the Nichiwa Maru.

Late in the afternoon, she was advancing westward on a scouting line formed by the wolf pack, when she sighted a plane dead ahead and about six miles (10 km) distant.

She immediately began to dive, but 90 seconds later, as she passed 110 feet (34 m), two bombs hit close aboard aft, sending the ship upward at an eight degree angle and causing extensive damage.

Operating in the supposedly inviolable waters of the Sea of Japan, the wolf pack attacked shipping and made exploratory attempts to enter Japanese harbors.

A few minutes later, Tunny approached within 5,000 yards (5,000 m) of the harbor mouth at Uppuri Wan but discreetly withdrew when searchlights located and then brilliantly illuminated the intruder.