Two loops - initially called 1 and 2 - were laid by the army. As they had cable laying ships for the controlled minefields in the area, this proved ideal. These loops were soon renamed Affirm (Loop A) and Baker (Loop B) (see map above). They were both of the three-legged design (see Indicator Loop technical page for details). Affirm consisted of three 3000 yard legs, spaced 120 yards apart (3000, 120 + 120); Baker was a 4000, 160 + 160 loop arrangement. Both were in water 15 fathoms deep. The tails were connected to the loop station on 21^st April 1942.

Loop signature record
This recording was made by seaman S. Handler at the Fort Williams Loop Receiving Station on 20^th December 1943 when USS New Jersey, (shown above), under the command of Capt. Carl Holden, made an inward crossing of Able Loop at 11.52 am. Visibility was high that morning (10 mi). The galvanometer being used was the GE Type OS-2, Serial No. #19, set at a shunt ratio of 125:1 and the sensitivity control set at zero. An injected voltage of 0.06 V to the Right was used for centering. The graph has the characteristic pattern of two crests and one trough, with the trough height (31 "lines" of flux) about twice that of the crests (18 "lines"). A "line" of flux is determined by the sensitivity control setting on the amplifier. In this case, the setting was zero which meant the sensitivity was left at it's base rate of 1000 lines per mm. The peak-to-peak distance is 18 + 31 (= 49 lines) which corresponds to 49000 Maxwells of magnetic flux linkage. This can give operators a idea of the size of the boat. For example, a 250 ton undegaussed U-Boat has a magnetic flux of 40000 Maxwells at 10 fathoms at this latitude. The speed can be calculated from the vertical lines (1 cm apart) and 1 cm = 1 minute. From start to finish took the 888 ft long USS New Jersey six minutes which corresponds to about 1.5 knots, assuming the loops are each 150 yards wide. Two weeks later, New Jersey headed off to it's first naval engagement - in the Pacific Theatre.

More problems
By 1^st June 1942, the operators were still having difficulty with signals from Baker and one of the operators tinkered with it to get it working. The repairman warned the operators "don’t do that". However, both recorders still proved erratic. Whenever the bay was swept for mines the recorders were disconnected so as not to blow their fuses. On June 22, 1942 a German U-Boat was suspected of making an inward crossing but due to faults in the other loop, it was not detected on its way out. The fault turned out to be from a loose terminals due to the continual doing/undoing so on the 27^th July (1942) a knife switch was installed. A litany of other problems were reported – paper jams in recorders, all three recorders unsatisfactory, sensitivity problems with galvanometers, telephone problems, teletype line down, clock not working. One fluxmeter – the OS-50 – was found to have a resistor in the amplifying circuit that heated up causing unsteadiness in the recorder preventing the needle from centering. The flux meters used were labelled OS-02-09 (on Able), OS-0-51 (on Baker). OS-50 became the spare. The amplifier attenuation settings were usually 1:1 or 1:5. In cases where sensitivity was low (from a weak signal), the ratio was changed to 1:125.

On September 22^nd, the station was officially changed in status from Naval Signal Station No. 6 to a loop receiving station (USN LRS). All of the signaling equipment thus had to be returned. This included 150 flags, one 12" searchlight, one rheostat and one typewriter. In return, four rifles were sent over to be "left loaded in strategic positions" near the loop station and the petty officer was henceforth required to carry a pistol.

Shift to Fort Williams
The first repairs to the cables were made on 26^th October. A break was found in the centre leg of Affirm and when this was repaired and relaid, the recordings improved. However, the army blasting continued, and the loop operators had to keep turning the flux meters off. This was hardly good harbor defence so the USN decided to relocate the loop station to Fort Williams. On 9^th November, USCG Pequot spliced the tail cables to the new location. Mr Simpson and Lt Sigafoos from BuShips (Bureau of Ships) inspected the station and approved it as ready for the grand opening. The new loop room was 8’ square – hardly enough to swing a cat. Seven men were stationed there.

By 8^th December the Navy decided that the cables were not functioning properly and relaid Affirm with ‘slack lay’ to reduce the pertubations caused from laying a cable too taut. The following lengths of Type 111 cable (in yards) were added to the cables: Affirm – inner 135, middle 300, outer 450. To Baker, 150, 135, 135 was added respectively. This seemed to improve sensitivity and they were now getting between 200 lines (Affirm) and 400 lines (Baker) although magnetic interference from minesweepers (up to 8 miles away) was creating havoc particularly with Baker’s recorders. Interference continued to be a source of problems at the start of 1943. Affirm was recovered and relaid nearby as loop ‘Able’. The army cables near Baker’s tail cable made balancing (centring) difficult. Various transmitters – such as those of the Harbor Entrance Control Post produced continual interference particularly on the 2150 kHz frequency. This caused fuses to blow in the resistor balancing box. On April 3^rd 1943, representatives of the NLDF (?) found that the public power supply was improperly grounded and fixed that easily. However all they could do about electrical storms and the Northern Lights was to install double pole, double throw switches. This seemed to do the trick. Things were looking up – the American Legion sent over a gift of 31 phonograph records.

Monthly reports
They were now recording monthly crossings of about 365 ships across Able and 37 over Baker. Also done monthly were loop resistance checks. The resistance – in ohms – were as follows: Loop Able B-R 19.71, B-W 19.18, R-W 19.84; Loop Baker 28.03, 27.79, 27.63. Recall that Baker loop was about 1/3 longer than Able, hence the increased resistance. The sensitivity readings varied between 77 and 240 for Able and 164 to 455 for Baker which were quite acceptable and gave good, clear signatures. As usual, all recordings were burnt at the end of each month (ie March recordings burnt at the end of May).

Severe magnetic disturbances continued to cause problems at all stations. A comparison of signatures between Fort Williams, Bailey Island and Cape Elizabeth during mid to late 1944 confirmed that atmospheric disturbances were to blame. But by then, it didn’t matter much.

On July 5, 1944, U-233, a German Type-X1B minelayer (90 m long) was sunk by aircraft and USN destroyer escorts USS Baker and USS Thomas after a 9 minute battle. It crawled its way 100 miles down the coast and entered Casco Bay where it finally sank. However, no loop recording was made. As the threat from German U-Boats waned, the loop stations were gradually wound down. What remains of them today is not known. But we’re trying to find out. If you have any idea, please contact Richard Walding or Dave Pierson.

* Text reference in paragraph 1: Butler, Gerald (2000). The Military History of Boston's Harbor Islands. Arcadia Publishing, 2 Cumberland St Charleston, SC 29401 USA. 128 pages, cost US$17 + US$9 p&h (overseas). Email: sales@arcadiapublishing.com. Web address www.arcadiapublishing.com. A fascinating book - 250 photos from 1860 onwards.