Fig 1

The T class conversion engines were, to the best of my knowledge, unaltered from when they were fitted in the unconverted submarine .Nominally 1250 bhp each side. Despite reports, the evidence indicates they were not converted to super charging, indeed the gain quoted was hardly worth the complication and expense.

Note the links for the alternative positions have to come from the battery isolating links thus preventing any possibility of placing the Nos 1 & 2 batteries in parallel with Nos 2 & 4 batteries.

Fig 1
Fig 1

Fig 2a and 2b

The two drawings Figs 2a and 2b are an educated deduction from the text from BR 1965 (1953) and anecdotal information from a former crew member. There may be errors in the placement of certain pieces of equipment but if this so, they are of such a nature as to make no difference to the understanding of the propulsion circuits of the T class conversion.

They are drawn principally to make the associated notes on BR 1965 and the First of Class trial data 1952 for HM Submarine TACITURN, more understandable, lacking the missing manual drawings.

Fig 2a
Fig 2a

There were two of these identical motor controller mechanisms per side, one for each tandem motor. They were installed longitudinally in the bottom of each fore and aft cubicle connected to their associated controller wheel by a control rod system, they were really a large multi-stage rotary switch.

Provision was made to work the controller directly with an emergency handle at the bottom of the cubicle, if the main system failed

The only difference between forward and aft controllers, was that the forward control wheel was smaller than the aft wheel, as shown in Fig 3c.

When in electric drive with the engine clutch open and the motor clutch closed the two mechanisms could be clutched together and operated in tandem by the large aft control wheel. This was a sensible arrangement when on high speed submerged electric drive with one watch keeper per side.

Fig 2b
Fig 2b

Fig 2c

Fig 2c
Fig 2c

This circuit shows the basic switches used in older RN submarines to place batteries, tandem motors and armatures, in series or in parallel to obtain a number of speed ranges. The 'T' class conversion used the grouper switch as shown to implement the battery group switches, the tandem motor group switches and the armature group switches. The first two, with duplicated knife blades for the heavy current, were operated mechanically by control wheels, the latter with single blades, by handle similar to the unconverted submarines but installed in a cubicle.

Examples of the armature group switch may be seen on the open switch board of the preserved HMS ALLIANCE.
Also on the ALLIANCE switchboards, the single change switch next to each main armature group switch, is nothing more than another group switch split in two with a section on each switch board, used for placing all four armatures, two per shaft, in series for the lowest speed range. Not used in my experience of some years.

Fig 3a

The only clear drawing I have from BR 1965 ('T' class submarine conversion) of a motor cubicle, is this one showing the control platform side of the starboard forward motor control cubicle.

It is clear from the text and the obscured general arrangement drawings, that the aft cubicle would have been much the same ,but with the starboard Tandem Motor Group Switch and a similar operating wheel and other small switches and indicating instruments. I also deduce the cubicle layout would have been as shown in the small sketch I have added below. The panel shown would have been at the LH shoulder of the operator facing the main control panel, with the blank LH side of the cubicle facing the gangway.

The two large combination ammeters (charge/discharge) were for No1 and No2 battery sections (on the starboard side) LH top.

They had maximum scale readings of 2000 amps charging and 10,000 amps discharging.

Fig 3a
Fig 3a

Fig 3b

The Port Switchboard - Control panel was essentially identical to this drawing. I have added the forward and aft motor control cubicles to illustrate the general layout. I understand that unlike the unconverted T class submarine, two electrical propulsion watch keepers were required per watch. An Leading Electricians Mate and an Electricians Mate. In addition the late Captain Coote when CO of TOTEM, reported he had a Commissioned Electrical Officer .See his book SUBMARINER, regarding this apparent waste of a highly skilled technical officer.

Fig 3b
Fig 3b

Fig 3c

This drawing is merely a magnified version part of Fig 3b to show more clearly the control clutch sighting window and the hand clutch operating lever .

Fig 3c
Fig 3c

Fig 3c


This table with data concerning the aft propelling motor, is associated in BR 1965 with the table that follows about the forward motor acting as a generator supplying the aft motor. It should be noted the speed figure I have added of 7.9 knots –350 rpm, is taken from the Snorting knots /rpm graph for two engines FIG VI TACITURN speed trial data. It should noted that the forward motor rpm are for the diesel/generator configuration and the after motor rpm is the propeller shaft rpm. The motor clutch being open.

A significant increase on the tabulated charging current of 500 amps, would have been achieved by a relatively modest decrease in speed, due to the speed/power cube law say 5.5 knot/250 rpm.

Table 6

At some snorting speeds excess power available from the generators may be used to charge the battery. Under these condition the Supply Pressure will rise gradually from 240 volts to the peak voltage for an Operational Charge. Any tendency for the (propelling ) motors to increase speed with the rising voltage should counteracted as far as possible by the use of the Shunt Regulators , and by grouping the Armatures in Series when necessary.

Snorting with Battery Charging - After Tandem Sets at 270 volts

Group Supply Pressure Speed
BHP per
Tandem Set
Time rating
across each
across tandem
Group 2
(Armatures in parallel)
270 270 350 630 Continuous
270 270 330 530 Continuous
Group 3
(Armatures in series)
135 270 305 420 Continuous
135 270 165 70 Continuous

Note - the maximum BHP per tandem set are the outputs obtainable from the after tandem sets with the forward sets developing maximum continuous current output as generators allowing 70 engine horse power for auxiliary load and 500 amps for charging.

With both shafts at 350 RPM then the submarine speed would have been 7.9 knots - taken from the Snorting knots/rpm graph for two engines Fig 6 'TACITURN'speed trial data, 1952. A significant increase in the tabulated charging current of 500 amps, could have been achieved by a relatively modest decrease in speed, due to the power/speed cube law and the tendency for snorting submarines at periscope depth to be effected by the speed related wave-making hull resistance experienced by surface ships.

This table is associated in BR 1965 is associated with the previous table on charging while snorting.

Table 8

Fwd Tandem Sets As Generators

connected in
Amperes per
Tandem Set
Parallel 310/480 220 2,600 Continuous
Parallel 370/480 220/270 2,600 Continuous
Series 165/270 220 1,300 Continuous

The outputs stated in Table 8 are the maximum continuous ratings permissible ,without overheating. The minimum speeds quoted refer only to the capabilities of the generators and the interpretation of the particulars given in the table being as follows:

Provided sufficient engine power is available the generators are capable of delivering the current values stated , over the whole of the corresponding pressure (voltage) and speed ranges; for example, with armatures grouped in parallel, 2,600 amps would be available continuously at 270 volt and 370 rpm.

The comment on available engine power may be in reference to rpm in snorting conditions



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