I do apologise for chosing this title, but as often as not the first two words were more often than not associated with one another, and the final word  has nothing to do with the Bard, Sheaksperes last play and a comedy of that name. 

MITS stood for Mutual interference Trials which were done during a ships HAT [Harbour Acceptance Trials] new builds and ex long refits.

I can best describe what a MIT was by reminding you that modern warships are packed full of devices, equipment and gadgets with every available space, in and on the ship up for grabs during the drawing board stages. Each department had it own champion vying for a chunk of the ship to be called theirs and theirs alone, but quite often having to settle for a compromise.

Of interest here, ours, the Communications Branches, was a group of officers cognisant with the working and requirements of communications equipment whether for visual signalling, electronic warfare, intelligence gathering and alalysis or wireless telegraphy was called URTS which meant User Requirements and Trials Section. URTS in the alma mater HMS Mercury, was dubbed 'X Section, the OIC called Commander 'X' with premises on the periphery of the sports pitches called High Trees at the far western end of HMS Mercury's foot print.

Anything remotely connected with communications went into the ship build under the URTS supervision and thereafter was set to work by the skilful and hard working dockyard branch knows as WSTG [Weapon Systems Tuning Group] under URTS watchful eye. All post fit subsequent trials were planned and organised by URTS and the MIT was the most important trial of all.

You will recall that communication aerial's for example were of several types, [a] those connected to the superstructure proper to mast and funnels called broadband HF/MF transmitting aerials [b] stand alone aerials connected to masts or on  yards from masts VHF/UHF for transmit and receive [c] stand alone aerials mounted forard above the bridge/flag deck level/ regions for Satellite transmit and receive [d] direction finding aerials MF/HF and in the higher frequency bands X,C,S etc all requiring dedicated position for D/F to function properly [e] whip aerials sited forard for VLF/LF/MF/HF reception [f] whip aerials sited aft for MF/HF transmission complimenting aerials under [a] above.  The very reason of [e] and [f] sitings were to minimise mutual interference where transmitters [aft] could interfere with reception arriving in the ship from forard aerials.

With space at a premium, imagine a missile system, say, the time expired SEACAT Missile system ready to strike at incoming aircraft or missiles fired from it where the launcher and associated radio aerial which are integral  mounted on top of the helicopter hanger roof aft,  and nearby, just a few feet away are four medium  powered whip transmitting aerials. What we have to guard against is mutual interference whereby a radio transmitter is being keyed which sends [by interference] erroneous signals to the SeaCat system  which then prematurely and without warning fires one of its missile and takes out a friendly air asset. This, an extreme example of mutual interference is what URTS has to prove wont happen before the ship gets a clean bill of health.  On an aircraft carrier, ammunition on deck waiting to be attached to airframes were known to be vulnerable from radio transmissions which had in the past detonated powerful munitions and caused many deaths and untold damage to ship and personnel and  materiel on the flight deck.

Now pardon my French, this is where the Shits bit comes in. A plan has to be drawn up by URTS involving every useable operating position within the ship using every piece of communications equipment on a whole range of frequencies and emissions and many different fixed aerial position, with other aerials nearby operational [radar navigation, gunnery/missile guidance radar etc] and not as a block but individually, with Decca, Loran and other navigational tools brought to play and then switched off at random.  Repeat serials where doubt existed which could so easily involve new days to be factored in and time after time it really did get up the backs of just about every ops branch person on board, not just communicators but personnel manning the TS [gunnery transmitting station], the sonar sound room, radar operators, AIO teams [action information organisation],  buntings running up halyards with Inglefield clips affecting sensitive instrumentation like 'met equipments etc etc including any adverse effects on the gyro compass. In jacks parlance it was a day[s] to be feared and obviously any defective equipment had to be fixed or replaced and the serial re-run until all serials were checked off as correct or within acceptable Limits of performance on a non interfering basis. The word shits is well understood and well worthy of being a part of this story.   HATS and SATS [harbour/sea acceptance trials] were [or could be] in many ways worse than a Portland work up!

On a DLG never mind a large vessels [and all needed to be checked] this resulted in a complan of over 500 serials all to be conducted to a very strict plan with no short cuts, some serials requiring a detailed write-up and a few with no reports necessary. It involved ships routine, watch changes, mealtime alterations, upper deck cleaning and working parties stood down or restricted to certain part of ship, and the whole crew was involved.  All leave was stopped until the MIT was satisfactorily completed. 

The result of the MIT could affect the operations in the ship until the next refit, because before transmitting on a given aerial it was necessary to know that, say, the 965 radar  rotation speed was below a certain known problematic speed. It was a command decision to determine which device took precedence on any given occasion.  There were many such ramifications brought to the attention of WSTG and URTS post MIT.


Tempest testing involved the MCO and the RWA [a RATT system widely fitted in many ships of frigate and above].

It involved searching for rouge DC [Direct Current] leakage from DC devices on the P/L [plain language] side of the on-line RATT equipment revealing sensitive classified  signals in the raw.

A telephone, the one right now in your home,  has two voltages an AC circuit and a DC circuit. Your telephone line is whetted with a 50V DC which BT supplies at the point of connection.  Your telephone is an analogue device [not emphatically a digital device] and whilst the majority of customers are connected in a street box coloured green, which converts your out going DC modulated analogue signal to a digital exchange, that is the point where your telephone call becomes a digital signal. The reverse also applies,  the exchange,  which  does all the clever things with routing etc and sends your call to your green box which is converted back to analogue for the final piece of wire to your house where it rings your analogue device. That's where the AC voltage comes in, it rings the bell which DC doesn't do!  The AC voltage comes from the 50V DC Whetted signal supplied by BT at source by a device known as an inverter and at a low voltage, enough to sound the incoming call ringer.

Now DC radiates and any phone was easy to be intercepted [eavesdropped upon] whilst still an analogue signal. That also applied to early day cell 'phones all of them analogue devices which could be freely monitored  on a radio receiver. Before the turn of the century [20th to 21st] analogue disappeared and cell phone used codecs and unless one knew them [which was an impossibility because they change by design so rapidly, one couldn't eavesdrop a cell phone. As in all things, eventually criminals found an answer but so did the manufactures and security favours the manufactures  who fortunately are a dozen leaps ahead of the criminals. The same went for land line phones as I have already said, namely that unless you can open a BT green box [and take my advice don't even try it as you will be nobbled in double quick time] to clip onto the analogue side of the digital converter, or you can connect to the over ground two core copper cable from green box to house, you wont be able to eavesdrop that number.

Back to my theme of DC, which  came from the terminal box [TT10] before the box had had a change to convert DC into a 1kHz signal, and as a DC signal as stated, one has only to get close enough to  monitor that DC signal to get the P/L.

The RN theory used to be that when alongside, particularly whilst visiting  a foreign port, a van,  with suitable equipment could park up on the same jetty and connect the radiated free-space  DC signal from the MCO into the back of his teleprinter in the van.  With that in mind, the navy instituted a regular test called 'TEMPEST' after first declaring a safe distance in that ship from the RWA racks and then to declare a "safe zone". No DC devices could be brought into the MCO into that imaginary circle which included, guess what, a telephone which even in a pussers ship is a DC device: but academic because the MCO 'phone was hard wired to the RIC [rating in charge] bay so no chance of it being used anywhere near the RWA area. The Naval Attache to the country being visited would suggest a suitable berth for the ship to his opposite number which would make it impossible for a van or any other device to eavesdrop RWA and say the RATT broadcast  being received which was the normal practice for the ship to maintain watch at sea or in harbour.   

This little sketch illustrates the vulnerable area of our on-line system which was part circumvented by making the electrical cable between the TT10 and the teleprinter as short as possible and that  they achieved this by sitting the teleprinter actually on top of the TT10 and having done that, to instigate the regular TEMPEST tests,  buoyed for security reason by that the magic unseen but known about circle of default viz the "tempest zone": inside it spelt danger and outside was considered innocous.


Here above, that secret weapon of denying radiating DC  to the outside world. Concentrate only on [A] the teleprinter printing out a P/L copy and [B] the TT10 converting the all telling DC signal unless it could be shut off.   That was done by the tiny short link you see at letter 'I'. Note 'A' is mounted on 'B'  allowing that little link common to ALL RWA outfits in the fleet also to RWB and RWC in submarine fits, to minimise DC radiations.

RWA's were common fits with few if any deviations and so too were frigate configurations e.g. Leander on Leander and destroyer, DLG on DLG etc  so the DC security safety circles were common to each class.  It was unstated in terms of visible markings but nevertheless fully understood by all MCO communicators.

The checks were simplicity themselves and on a forewarning signal a greenie would arrive with a meter which measured  our radiation on the extremity of the security circle.  Little ever changed and I can never remember getting a failed or altered certificate.

Thanks for viewing.