Torpedo Deflection Sight Mark VII

Periscope model

Periscope model

The Torpedo Deflection Sight Mark VII (originally the "Periscopic Torpedo Deflection Sight") was a British purpose-built Torpedo Deflection Sight.

Manufactured by Vickers, they were originally called the "Periscopic Torpedo Deflection Sight" but were re-designated to avoid confusion with the T.D.S. Mark IV. Unlike the Mark IV, whose periscope looked out through the horizontal view slot of a torpedo control tower, the Mark VII's protruded through the roof and was for times when gun blast was so heavy that the control tower slots had to be shut.

The Mark VII apparently lacked any gyro compass input, and so if the Mark IV were unavailable to provide target gyro bearing when the slots were closed, this would come from the 15-foot torpedo control rangefinder, which was Evershed controlled from the primary control position.

Design

The sight had a periscope of 2.5 power with a field of 15 degrees. It worked as follows.

The topmost of three cylindrical rings was fixed to the overhead and showed relative bearing. Beneath that, a gyro ring could be revolved by a hand knob. The bottom ring was for deflection of the various torpedo settings. It moved with the periscope, but could move relative to it by a worm screw driven by a hand knob. The gyro and deflection scales were connected by gearing so that when the deflection was altered, the gyro angle moved moved in the opposite direction the same amount.

The user would dial in the deflection and the gyro angle would rotate the opposite direction to indicate the required gyro angle. A prism set in the device would permit a small area in the bottom of the view to show the gyro angle and the deflection.

The cylinder which contained the deflection lines was cleverly offered in that each position seemed to offer four or even five torpedo speeds, and the scale had two or three positions to offer.

Alterations

By mid 1919, two of the sights trialled in Courageous, and a report was sought to see if changes would be required in three which were on order for Hood. The report found that:

• the sight needed to be able to rotate in elevation to be workable while rolling or listing
• it was excessively prone to internal fogging, even if kept set up for just a short time
• it required graduations for the 35-knot torpedo speed
• it requires a rubber skirt of similar device to keep water from leaking into the space it was housed
• an in-built means of seeing deflection and gyro angle scales seems unnecessary, as these can easily be read off the external scales

It was resolved to remove the scales referred to in the last item for future deliveries. The alterations eventually made for Hood resulted in the T.D.S. Mark IX.