As has been frequently mentioned, the science of modern oceanography had its inception approximately one hundred and eight years ago with the appointment of Lieutenant Matthew Fontaine Maury, U.S. Navy, as Officer in Charge of the Depot of Charts and Instruments, the forerunner of the present day U.S. Navy Hydrographic Office. Maury’s Track Charts, Wind and Current Charts and his book, Physical Oceanography of the Sea, were all notable contributions to the application of oceanography to the successful operation of vessels on the high seas. The program was a collaborative one, with the merchantmen forwarding the data concerning sea and swell, winds and currents, and Maury, in turn, preparing and issuing the Sailing Directions, Wind and Current Charts and similar publications. In addition to these more or less routine observations, Maury received oceanographic, hydrographic, and meteorological observations from surveys either financed by private enterprises or sponsored by the Navy. The expedition headed by Wilkes, the expedition to Japan under the leadership of Perry, and the North Pacific Survey Expedition under the direction of Ringgold and later Rodgers are examples of this source of data.
In the year 1928, the Navy Department was approached by the National Academy of Sciences concerning the part the Navy could play in furthering the collection of oceanographic data. In response, the Honorable C. D. Wilbur, then Secretary of the Navy, appointed a special group known as the Schofield Board and requested that they investigate the problem with interested scientific and government officials. The Board, following a period of discussion and study, submitted a report embodying two suggestions. First, that a specially equipped vessel, or vessels, be assigned to this task, and second, that the program of observing and recording oceanographic data be, in part, carried out by specially trained observers and shipboard personnel on the regular voyages of naval vessels. This report enabled the Hydrographic Office to purchase specialized equipment to implement the second suggestion, and various vessels, such as the Hannibal, Bushnell, and Louisville, were assigned to undertake these observations during periods at sea. Scientific personnel from various government and private activities took part in these survey programs.
The success of the program is indicated by the fact that over 5,000,000 oceanographic observations were received and that cooperating observers, the Merchant Marine, the Coast Guard, and the Navy are now submitting over 200,000 observations per year.
With the establishment of the Division of Oceanography in the Hydrographic Office in 1946, the oceanographic programs of the armed forces were centralized in one agency.
In conjunction with this centralization, the Chief of Naval Operations directed that two vessels be taken out of moth balls and assigned the primary mission of oceanographic survey. In response to this directive, the U.S.S. San Pablo (AVP-30) was commissioned at the San Francisco Naval Shipyard and the U.S.S. Rehoboth (AVP-50) at the Philadelphia Naval Shipyard. These two vessels, formerly Barnegat class seaplane tenders, were, early in 1948, assigned to the technical control of the Hydrographer and the administrative control of the Commander Service Force, U. S. Atlantic Fleet. Thus, twenty years later, the first recommendation of the Schofield Board was realized.
Recently the designation of the San Pablo and Rehoboth has been changed from that of seaplane tender, AVP, to AGS or Auxiliary General Survey. They are 310 feet long with a displacement of approximately 2,750 tons and carry a crew of about 150 men and 10 officers. Normally, from two to four civilian scientists participate during each of the cruises.
Considerable modification was required to convert the ships from seaplane tenders to vessels suitable for their new primary mission, that of oceanographic and hydrographic survey programs. Laboratory and drafting spaces, winches and specialized survey equipment, facilities for developing and printing photographs, and berthing facilities for the participating scientists were required. Also, of a more difficult category, it was necessary that the enlisted complement, normal to the AVP, be revised to include the ratings applicable to the new technical duties. These additional ratings included draftsmen, quartermasters, electronics technicians, and aerographers mates.
As to the laboratory space, two compartments were modified to include the necessary work benches, sinks with fresh and salt water, cabinets and storage spaces and racks to hold the various pieces of specialized equipment. One space, that on the main deck, port side, covered by the after end of the boat deck, is used for the general handling of the overside equipment, processing of the various records and for the analyses of the water samples for oxygen content. The lower laboratory, one deck below the previously described space, is reserved for salinity analyses, preparation of various chemical reagents, and the study and preparation of the biological samples.
One large compartment, well forward on the second deck, was converted to a drafting room and office space. Adequate desks, chart tables, file cases, and chart stowage were provided. It is here that the various calculations associated with the oceanographic observations are made. Also, smooth plots including the sonic soundings, geographic location of the various observations, and the profile plots for the various variables against depth are maintained.
One of the five-inch gun mounts was removed from the after weather deck and a photographic laboratory constructed. This laboratory was supplied with negative and print developing and washing equipment, enlargers, and dryers. Also, an ozalid machine was provided to facilitate the reproduction of illustrations and graphical material accompanying reports of the survey programs.
In order to handle the various pieces of overside equipment, a new winch was designed by the Hydrographic Office incorporating hydraulic control. This winch, semiportable in construction, carries 20,000 feet of 5/32", 7X7 stranded stainless steel wire and was so designed as to hoist and lower the 20,000 feet of wire, eleven water sampling bottles (Nansen), and a 250-pound weight at an average speed of 500 feet per minute. While hoisting or lowering, an automatic tension feature allows the wire to be paid out and relieved of any excessive strain. An infinite number of speed positions are available between creeping speeds of 10 feet per minute to full speed in either direction.
Immediately abaft the photographic laboratory, a large mine-sweeping winch was installed to permit deep sea anchoring and to provide facility for lowering heavy pieces of survey equipment. This winch carries 3,600 fathoms of one-half inch wire rope. The U.S.S. Rehoboth has been successfully anchored in 2,000 fathoms of water using a five hundred pound Danforth anchor. Both vessels were anchored in 1,000 fathoms for a period of approximately twenty-four hours. During this latter period, deep sea sampling techniques, referred to as “oceanographic stations,” were utilized, every four hours. Also, bathythermograph observations were taken every fifteen minutes. Although the bathythermograph was designed as an instrument for recording temperature against depth from a ship underway, it serves admirably from a vessel at anchor or lying to. Perusal of the various technical journals indicates that the two periods of anchoring, that in 2,000 fathoms by the Rehoboth and the twenty-four hour period for both vessels, establish records for U.S. Naval vessels.
The sea water samples and temperatures at depth were obtained with Nansen bottles and attached deep sea reversing thermometers. The Nansen bottle is attached to the wire and lowered to the desired depth. A messenger sliding down the wire strikes a release mechanism and the bottle rotates through 180°, closing valves in each end, thus entrapping a water sample. Two types of reversing thermometers are used. One, the protected, records the temperature at the depth of reversal. The other, the unprotected, which is subjected to hydrostatic pressure, measures the temperature plus the pressure effect. The difference between the two readings, following various simple corrections, will yield the depth of reversal. Racks for the Nansen bottles with their associated thermometers are provided along the port side of the photographic laboratory and the port side of the weather deck laboratory.
The water samples, as taken in the Nansen bottles, are analyzed for dissolved oxygen and for salt content. Both of these variables aid in the identification of the various water masses traversed, e.g., Gulf Stream, Sargasso Sea, Mediterranean, etc., and the salinity, with the temperature, can be converted to density. From an accurate knowledge of the density at various geographical locations and depth of “levels,” surface and sub-surface current charts may be constructed. Other routine observations include sonic soundings, bottom sediment samples, transparency of the water, color of the water, sea and swell, and meteorological data.
One officer, with postgraduate training in oceanography at the Scripps Institution of Oceanography, has been detailed to each vessel and designated as the Hydrographic officer. The enlisted men assigned to the Hydrographic Division receive training at the Hydrographic Office in all phases of the survey operations. These men have become very proficient in their work. With little more than technical advice and assistance from the professional oceanographers aboard, the vessels can conduct the oceanographic stations, make the chemical analyses, and complete the preliminary calculations.
With the emphasis on accurate position fixing for the sonic soundings, the data required for detailed delineation of the sea bottom topography, and for the geographic location of oceanographic stations and other observations, accurate and dependable methods for navigation were required. Both vessels were equipped with Loran (Model (DBE), RDF, DRT, and SG Radar. Also, for the sonic soundings, two NMC-2 echo sounders were installed on each ship. A transducer was placed on either side of the keel with the recorder units so wired that each recorder could receive impulses from the port or starboard transducer. Also, one recording unit was slaved with the other in order that, during periods of adverse weather conditions, the two transducers were simultaneously energized, increasing the probability of receiving an echo. These echo sounders were modified to record 4,000 fathoms. Soundings are recorded continuously on the tape as well as a reading, every five minutes, being entered into a log book. The navigator’s track chart is adjusted daily, plotted as a “smooth” plot, and soundings of ten minute intervals entered on this smooth plot.
Since the inception of the program, the two vessels, designated as Task Unit 49.6.5, have steamed a combined total of 103,000 miles, and taken 470 oceanographic stations and 9,000 bathythermograph observations.
These data, supported by the routine meteorological observations, not only add significantly to our knowledge of the distribution of variables in the oceans, but also are applicable to theoretical and practical studies so necessary to understand the “why” of the phenomena to be found in oceanic areas and to utilization of this information to the increasing advantage of the navigator, both naval and maritime.