[5] During her third cruise, which she completed with her return to Pearl Harbor on 14 November 1952, Charles H. Gilbert operated in conjunction with a United States Navy flying boat to study the effectiveness of using aircraft to assist ships in scouting for tuna in the central Hawaiian area.

[9] She battled winds of fresh gale force, and this unfavorable weather combined with an apparent seasonal scarcity of fish and limitations of her design prevented her from carrying out many of her cruise objectives.

[11] In addition, she made seabird observations, noting a relative absence of shearwaters and the presence of jaegers and other skuas – never recorded in the mid-Pacific prior to 1952 – which suggested irregular meteorological and hydrographic patterns.

[13] In addition, she brought back some live, small yellowfin for fish-attractant experiments at the University of Hawaii research station at Coconut Island off Oahu[12] and collected a number of unusual or rare biological specimens, including of the snake mackerel made famous by the 1947 Kon-Tiki expedition.

[15] During her 10th cruise – a four-day voyage that concluded with her return to Pearl Harbor on 26 March 1953 — Charles H. Gilbert tested the difference in handling steel-wire and cotton longline fishing gear off the Kona Coast of the island of Hawaii and southwest of Lanai.

[33] The two vessels had to scrap plans to explore waters any farther than slightly to the east of 160 degrees West due to rough weather,[31] and they returned to Pearl Harbor on 21 December 1954 after a three-week cruise.

[41] Charles H. Gilbert tested electronarcosis on four schools of skipjack as a means of quieting them to avoid injuring them during tagging, but achieved erratic results that suggested the technique lacked efficacy.

Charles H. Gilbert departed Pearl Harbor for her 27th cruise on 17 March 1956, bound for the North Pacific and another check on springtime albacore abundance and related water conditions there, part of the ongoing several-year effort to establish the seasonal distribution patterns of the fish.

[73] That day, POFI scientists released about 12,000 live Marquesan sardinellas she had brought back into Pokai Bay on Oahu in the hope of establishing the species in Hawaii to increase the chronically short supply of bait fish there.

[92] Charles H. Gilbert left Kewalo Basin on 8 or 9 October 1958 (source gives both dates) to begin her 42nd cruise, intending to make further observations of skipjack feeding behavior in Hawaiian waters.

[93] The turbulence created by the submersible observation platform greatly interfered with its ability to support effective underwater photography and film-making, and it was removed from Charles H. Gilbert after her return to port.

[96] Cape Falcon′s catch was disappointingly small, and Charles H. Gilbert sighted only half the number of schools found during the 1957 and 1958 seasons, with fish averaging only 6 pounds (2.7 kg) and difficult to chum to the vessel.

[106] She filmed the behavior of skipjack from her observation chamber;[107] investigated a temperature discontinuity she encountered south of Molokai;[106] and longlined and made plankton net tows to survey the types and abundance of marine life in various water conditions.

[1] Charles H. Gilbert got underway on 12 October 1960 for her 50th cruise with an embarked team of scientists led by a geneticist, headed for the equatorial South Pacific to investigate skipjack and yellowfin biology.

[127] She searched the French Frigate Shoals and Johnston Atoll for live bait but found it very scarce, and she also encountered few tuna, finding a concentration of small schools only in an area 300 nautical miles (560 km; 350 mi) south of Honolulu.

[147] Noting that any sizable drifting object tends to attract sea life and can create good fishing conditions, especially for mahi-mahi in Hawaiian waters and for tuna in various parts of the Pacific,[148] the Honolulu Laboratory decided to study this phenomenon.

She departed to begin her 64th cruise on 9 April 1963 with oceanographers embarked to study large oceanic eddies — 20 to 50 nautical miles (37 to 93 km; 23 to 58 mi) across and rotating once every ten days – which USFWS scientists hypothesized existed southwest of Oahu between the Hawaiian Islands and the North Equatorial Current.

[158] Charles H. Gilbert then conducted the second phase of her 65th cruise from 6 to 20 May 1963,[157] resuming the collection of live fish within 45 nautical miles (83 km; 52 mi) of the south and west coasts of Oahu.

[163] During her cruise, she made 12 surface plankton tows; occupied five night-light stations; collected blood samples from 12 bigeye tuna, two skipjack, and a blue marlin; released a combined total of 1,000 drift cards in the study area and in the lee of Oahu, Molokai, Maui, and the island of Hawaii;[163] tested two small-mesh gillnets, both 12 feet (3.7 m) long and 50 feet (15 m) deep, for the Albacore Ecology Program, catching no fish; ran her recording thermograph and barograph continuously while at sea; and brought two live mahi-mahi back to Kewalo Basin for research.

[165] In Phase I of the cruise (21–25 August 1963)[165] — during which shipboard and scientific activities were photographed for a television program – she located a thermal dome associated with the eddy in the vicinity of 20°25′N 157°26′W / 20.417°N 157.433°W / 20.417; -157.433, launched drogues about 25 nautical miles (46 km; 29 mi) from it, and tracked them over the next three days.

[173] She launched the raft on 22 February 1964 in an upwelling near 00°09′N 149°35′W / 0.150°N 149.583°W / 0.150; -149.583 and allowed it to drift for 193 hours 31 minutes before recovering it on 1 March 1964 at 00°10′N 159°12′W / 0.167°N 159.200°W / 0.167; -159.200, over which time it moved 576 nautical miles (1,067 km; 663 mi) due west at an average speed of 2.5 knots (4.6 km/h; 2.9 mph).

[172] She also made daily Secchi disk and Forel color readings while drifting; preserved flying fish which landed on her deck for stomach analysis; and recorded sightings of tuna schools.

[192] Charles H. Gilbert operated off the leeward coast of Oahu from 7 to 24 June 1965 for her 83rd cruise, testing plankton and neuston nets in hauls at 68 stations to determine their effectiveness in collecting larval and juvenile tuna.

[193] On 23 July 1965, Charles H. Gilbert set out on her 85th cruise, bound for the west coast of Mexico to gather data that would help USFWS scientists determine whether and to what extent the skipjack found in the California fishery and that of Hawaii represented a common stock or two different subpopulations.

[203] After Charles H. Gilbert arrived on the scene, she used pole-and line fishing techniques to land the young bigeye tuna, and returned to Kewalo Basin with 89 live ones, all about 20 inches (510 mm) long and around a year old.

[207] The BCF's acting area director in Hawaii said that "A whole generation of oceanographers and fishery biologists received their practical training in research aboard Charles H. Gilbert," adding that "She has made some real contributions to science.

[210] She also spent two weeks (from 15 to 28 November 1967)[211] making 101 bathythermograph lowerings to determine the thermocline structure around the Hawaiian Islands, discovering two major eddies, both 100 nautical miles (185 km; 115 mi) in diameter,[210] rotating at 1 to 2 knots (1.9 to 3.7 km/h; 1.2 to 2.3 mph),[211] and lying southwest of Hawaii.

[213] Her first 24 longline stations, off Kailua-Kona on the island of Hawaii, demonstrated the presence of a current flowing east-southeast toward the southern portion of the Kona Coast, as well as of a counterclockwise eddy in the northern part of the study area.

[220] She operated in the equatorial waters of the eastern Pacific Ocean about 1,700 nautical miles (3,100 km; 2,000 mi) south of San Diego to collect skipjack and yellowfin for subpopulations analysis.

[222] She returned to Honolulu with 259 skipjack[223] and 42 yellowfin for the subpopulation study,[221] her personnel reporting the best fishing in clear, blue water with a temperature of 25 to 28 °C (77 to 82 °F), a thermocline at a depth of 40 to 100 meters (131 to 328 ft), and currents setting easterly.