The Hornby 0-4-0 Sentinel Diesel Shunter (DCC ready) is a tiny locomotive, especially when you compare it against an 08 Class. Hornby have cleverly designed this loco with decoder installation in mind, and when you first set your eyes on the Sentinel, it seems that there wouldn't be enough space for one. So, what to do... 1. Obtain a 4 pin decoder. I used Hornby's offering for this, Hornby catalogue no. X9659. 2. Flip the loco over onto it's roof and identify the screws that need removal. These are marked below. Note that there is one hidden under the NEM coupler pocket on the short hood end. To remove the coupler pocket, the brake rigging needs to be lifted, shown green. It can be unclipped where the blue arrows are and lifted back towards the centre of the loco, but don't lift too far ! 4. The coupler and three screws removed. The pic shows which screws belong where in relation to the locomotive. One short and two long. 5. Using a small flat blade screw driver, carefully lift out the handrails from the front and rear valance/buffer plate and along the body valance. The hand rails at the short hood end besides the cab pop out vertically. 6. With the body off, this is what you have. Be careful with the small marker lights. They will come out on the short hood end, as I found out ! 7. To expose the decoder socket, a small flat blade screw driver is used to lift off the cab controls casing. Lift this gently moving around all three sides. 8. With the cab control casing off, the decoder socket is exposed. 9. A close up of the decoder socket. make a note which end goes where, so that the dcc decoder is not put in the wrong way round. Note the small arrow. 10. Attach the decoder in place. If using a Hornby decoder, you will note that the colour of the wires match on each side of the plug. 11. Test fit the decoder. Note how the decoder sits on the blue section of the chassis. The blue section is plastic and the chassis is cast. 12. To prevent any future shorts, I chose to wrap the decoder in some insulation tape. Carefully place the wires back in the void under the cab controls. 13. Place the cab control casing back on, remembering not to pinch any wires ! 14. I chose to paint the cab controls grey and fix a driver into place. The Dapol/Airfix figure had a good portion of his legs removed to fit under the cab roof and his arm has been cut and shut as to allow him to meet the controls. 15. Fit the body back on and reconnect the handrails. This will hold the body down so you can flip it over and fit the three screws. Pop the coupler back in and your ready to go, well atleast to program the locomotive ! Loco fitted, programmed and weathered ! Cheers, Gary.