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Genesis

NDRC

NDRC (National Defense Research Council) setup various subdivisions for scientific military research.

On October 1, 1940 The Army Signal Corps Technical Committee proposes a Precision Navigational Equipment for guiding Airplanes with the following requirements to the microwave committee of the NDRC:

a. General: It is desired to have precision navigation equipment for guiding airplanes to a predetermined point in space over or in overcast by radio beams, detection apparatus, or direction finders.
b. Distance: Maximum possible. Five hundred miles desired.
c. Altitude: The ceiling of present heavy bombers; about 35,000 ft
d. Accuracy: the greatest accuracy obtainable. One thousand feet at 200 miles is desirable.

Dr Alfred Loomis, Chair of the Microwave Committee, submits the Army Signal Corps proposal in the October 1940 meeting. Project was accepted and established as Project 3.

Division Three was headed by Mr Melville Eastman. The early staff included:

Jack Pierce, ionosphere researcher,
Professor Jay Stratton of MIT, radio wave propagation
De Curry Street, a past-master at handling electronic circuits
Dr Fletcher Watson, astronomer

Dr Alfred Loomis was not on the staff but his early interest in scientific military research had a strong influence on the group and personally financed some of the early projects and kept them going until the Government agencies were established. Dr Karl Compton, President of MIT was also on the leader group.

Radiation Laboratory was sub-divided into divisions. Division 11 had a blanket assignment - "Develop aids to navigation"

During December 1940, there were numerous activities from division 3 including:

Coordination sub-Committee's first recorded minutes to arrange for procurement and field testing of one pair of transmitting stations and suitable navigation equipment outlined in original proposal.

The members were representatives of several large electronic manufacturers.

Although the precise method of synchronizing the transmitters had not been determined and no agreement had been reached concerning the most practical method of constructing a suitable navigator's receiver-indicator, the committee initiated purchases of $400,000 worth of equipment.

After receiving various suggested site locations, the decision to approach the Coast Guard about using the abandoned lifeboat stations at Montauk Point, Long Island, NY and Fenwick Island, DE.

Original experiments of NDRC Division 11 were attempts to develop a high frequency pulse transmission system based on Radar and the Laboratory's extremely fragmentary knowledge of the British GEE system.

The laboratory staff under the guidance of Mr Eastham drew up plans for a new type of transmitter and receiver based on the principles of television using the cathode ray tube to display the pulses generated by the transmitters. Contracts were let to GE and Western Electric to the amount of nearly one million dollars.

Navigation Group formed, under the direction of Eastman and under the technical direction of JC Street. Although assigned the receiver-indicator, this group was interested in the basic concepts of the whole system. By summer, the Navigation Group took over the lead from the microwave committee.

During May of 1941, NDRC receives permission from the Treasury Department to occupy the two inactive USCG Lifeboat stations as experimental sites.  Permit was for the period of 1 Apr 41 through 31 Dec 42

Two transmitters were quickly constructed during early summer and capable of transmitting the thirty-three and one-third pulses per second on any frequency from 8.5 MHz down to 2.9 MHz. The output power was 5 kW peak.  The transmitters were installed at the two locations and the receiver setup at Bell Telephone Laboratory's Transoceanic Monitor Station at Mannahawkin, NJ. The installations were protected by shielded rooms of solid copper, rudimentarily air-conditioned, and costing seven to eight thousand dollars each.

No attempts to synchronize the transmitters were made as a grid-laying hyperbolic system was not the original proposal.

Initial Testing June to August of 1941

RadLab Test Summer 1941

  A station wagon, with the receiving equipment installed drove as far west as Springfield, MO. As expected from the RADLAB group, the skyway signals were fairly strong and relatively stable. The lower frequency skywaves were more stable at night and the higher frequency skywaves more stable during the day. The tests also demonstrated that the medium frequencies could be used for a truely long range navigation system, but the potential accuracy could only be estimated. Also noted was a circular sweep indicator could not be used satisfactorily for making measurements on the order of one microsecond.

  In the late summer of 1941, A.G. Touch of the BAC visited the RADLAB. This was timely as all the attempts at using a circular sweep proved awkward, if not impractical. Touch described the GEE system in a cursory fashion, but left the group with two salient points:

1. Accurate measurements to better than 1 microsecond could be made with portable equipment.
2. A multiple trace indicator providing a means of matching pulses in time on delayed sweeps was a practical means of accomplishing this.

  A two trace indicator capable of direct comparison by superposing the displayed signals would be necessary.

   Oct - Dec 1941 ...

   Evaluating the first two-trace indicator at Montauk Point, they discovered the 5 kW peak signals from Fenwick would be ample for direct synchronization, especially on the lower frequencies.  Fenwick Island achieved occasional synchronization, but unable to keep transmitters on air with any regularity or obtain maximum reception of Montauk's signal at any time.  Synchronization was achieved at Manahawkin Monitoring station because the two signals were nearly equal in amplitude.

  Refinements came later. During these tests the 5 kW signal from Fenwick were ample for direct synchronization on the lower frequencies (1-2 MHz). 

Initiated work on 100 kW peak pulse transmitters with plug-in tank circuits for operations on several frequencies in the MF band. At this power they estimated direct synchronization and ground wave ranges of 600-700 nm over seawater and skywaves out to 1300-1400 nm.

One of the most serious shortcomings in the Loran receiver-indicators was measuring time differences of two unequal pulses. A relatively simple method of differential gain control was developed completing the basic evolution of the receivers that were reproduced by the tens of thousands for use during the war.

The Navigation Group came to the unhappy conclusion that high frequency; short wave experiments were not producing any efficient or significant results despite the large expenditures of time or money.  They decided the long range features of the medium frequency should receive their full attention. The British GEE system was a high frequency system and no need to duplicate their system.

The original Project 3 work was abandoned.

Jan-Jun 1942

A few months before the end of Project 3, the entire field organization, including the manager (W.L. Tierney from Bell Labs) was transferred to the Radiation Lab Navigation Group. As this field organization worked out its own purchasing, receiving, and shipping programs, authority to continue these activities was granted by the Division of Industrial Cooperation of MIT. This continued throughout the life of the Loran Group and facilitated the carryout of numerous critical field programs as well as hasty procurement of much equipment for the services.

The Loran Group was designated Division 11.

Because the original low power and variable frequency transmitters were used for the test, the 5 kW ground waves were not expected to be, nor received at Bermuda. Excellent skywave measurements were made in Bermuda with an average error in the LOP of about 2.5 miles. They changed rates to cause the remote signals to “drift” on the indicators. Further investigation demonstrated the same frequency could be used for seven discrete increments in the repetition rate in steps of 1 part in 400 different rates.

Radiation Laboratory carried out a series of high power (30kW - 50 kW) medium frequency tests in the 1 to 2 MHz range. Pierce and Stephens visited Bermuda where the low power (5 kW) medium frequency tests over water. 

In March, 1942, Melville Eastman considered the propagation of the 2 MHz test results promising enough to meet with the representatives of the Joint Chiefs of Staff and proposed a series of test units along the Atlantic seaboard to determine the maximum range of the waves and their possible development into an aid to navigation. The final plan as presented was the NDRC would construct, install, and operate the stations and the results would be given to whoever was most interested. The Army showed little interest, but the Coordinator of Research and Development for the Secretary of the Navy felt it was worthy. The outcome was the joint decision for tests along the U.S. and Canadian Atlantic Coasts.

In May, 1942, Don Fink returned from Canada with the promise and support of the Canadians and assurances from the RCN necessary for the Canadian test units, except technical equipment and technically trained installation crews. The Navy Coordinator of Research and Development had received no concrete information as to the practicability of the schemes or information on how the establishment of the test demonstration stations was progressing. Feeling there was a definite possibility that new long range navigation might be developed as a result of the projected tests, and perhaps feeling that some Naval guidance and assistance was required by the Radiation Laboratory Division 11, he took steps for closer observation.

Vice Chief of Naval Operations requests the assignment of "qualified" officer possessing radio and electronic experience. This is a special duty to the VCNO. The project was so secret that neither Rear Admiral H.F. Johnson, Rear Admiral C.A. Park or Captain Irving L Gill, Chief, Communications Engineering Division, USCG , the officer recommended, has any idea as to the nature of the assignment other than it related to an electronic navigational device which might have some war importance.

The Lighthouse Service operated and maintained radio beacons, a WWI radio aid to navigation. In 1939, the CG absorbed the Lighthouse Service. This placed the shore side direction beacons operations, maintenance, and expansion under the U.S. Coast Guard.

Lt Cdmr L.M. Harding, USCG, was detailed to VCNO and ordered TAD at Cambridge, MA the first week in Jun.

First Trials

First Trials June-July 1942

Using only one baseline, the USS Manasquan on weather patrol was probably at one of the three patrol areas shown, Bravo, Delta, or Echo.  All three meet the over 1300 nm distance from Fenwick.

The first two high powered transmitters (100 kW peak power) were installed at Montauk and Fenwick.

The first Radiation Laboratory timer, Model A, was installed at Fenwick and direct synchronization was established.

The Royal Canadian Navy had already agreed to supply enlisted personnel to man the two Nova Scotian stations under construction, so several men were selected to train in operation and maintenance at the Radiation laboratory, and also at the two stations in operation at Fenwick and Montauk.

Improved model receiver-indicator with multiple rate selection and differential gain control was installed in a Navy blimp from Lakehurst NJ for a full scale demonstration of the Loran system. Later that month another receiver indicator, and observers, was deployed on the USS Manasquan, a CG weather ship. The frequencies used for this test was 1.95 MHz and 7.5 MHz, the former gave the better reception. Only one baseline and one set of LOPs were available for this test.

USS Manasquan, a Coast Guard vessel doing weather patrols, had Loran receivers installed and the Loran reception tests were conducted by two RadLab engineers, Davidson and Duval. Duval was a recent addition and a former Naval Officer and navigator. The results were completed by 17 Jul 42.

Lt Cmdr Harding reviews the test results from the USS Manasquan, ground waves up to 680 miles in the daytime and effective to 1300 miles using skywaves. Harding quickly notified VCNO and CG Admiral Furer of the results. He had a strong recommendation for a full trial with the addition of the third station to complete the chain providing the second hyperbolic line.  The results were so promising, a full scale test was ordered by the Navy.

The full scale test expected the signals to reach Cape Farewell Greenland and skywaves reaching the Azores.

The pace quickens as we move forward.

Several joint Army-Navy-NDRC meetings were held to discuss the progress of the system and formulate plans for the most expeditious introduction of Loran to service use.

The Radiation Laboratory agrees to have four stations and three lines of position available for a full scale service test on 1 Oct 1942.

The Navy requested the NDRC to purchase equipment that included future installations in the Aleutians and North Atlantic.

- 250 model LRN-1 and LRN-1A shipboard receiver indicators
- 62 100 kW transmitters
- 50 navigator trainer units
- 80 transmitter timers
-50 receivers for transmitter timers

Total Cost $1,250,000.

Airborne receiver development was initiated by RadLab under NDRC contract with GE in Bridgeport CT. This was turned over to the Aircraft Radio Laboratory of the Signal Corps at Wright Field. The Army requested the RadLab cancel all work done by GE, even though they had already finished one excellent model, and gave the job to Philco. That decision set the AN/APN-4 airborne receiver-indicator back a year.

A new type of shock absorber, with a period of 2 Hz, appeared so sloppy but proved to absorb the most violent shocks during battle.

COMLANTFLEET stationed a number of noncommissioned personnel to receive the receivers and install them on carefully selected ships.


Full Scale Service Test