The Fissure Detector depends for#its operation upon the fact that electric current flowing through a rail is compelled to pass around any fracture, inclusion, or separation in the metal. In the detector car, tie power plant for the detector equipment consists of a specially designed double commutator 6,000-ampere, 2-volt DC generator directly coupled to a 50 hp engine. Current from thk generator is carried by heavy busses to brush units located on either side of the car. In operation the car passes along the track at about 6 mph, with 2,000 to 3,000 amperes glowing through each rail. The current is sensed by the pickup unit, amplified and sent to a recording table, which consists of a moving roll of paper and nine pens (like a polygraph or lie detector). The top pen (landmark pen) is marked by the car's operator to indicate mileposts and other landmarks, the middle two pens record angle bars (rail joints). When the car passes over a fissure, and indication appears on the record. Three recorder pen relays are connected to the output of the amplifier and adjusted to different values of plate current, thus giving an indication of the size of the defect. Other relays are provided to operate paint guns and the defect area is automatically marked with a spot painted on the rail. The operator notes the record, sees the spot painted on the rail, and stopping the car, backs up for a hand test, applying 1,500 amperes to the suspected spot. Examination of the spot with a galvanometer can determine the size of the fissure within a few percent. The car can also find split heads, horizontal fissures, compound fissures, pipes, cracked webs, broken bases and other defects.

The car in front of it has C&NW reporting marks, but also has Genesee & Wyoming painted on the letterboard. It appears that it was numbered C&NW 404, later C&NW 440 and named "Philip R. Hastings".

As built, the RDC3 consisted of a 17 foot Railway Post Office, a 17 foot express room, and a 40 foot, 49-seat passenger section. Some RDC3's were built without RPO apartments, but used an identical carbody to those so equipped. Of the five RDC3's originally owned by the New Haven, #'s 126 and 129 migrated to Pennsylvania DOT ownership, rhere they were converted to all-coach layout. At first they were assigned to Pittsburgh PAT service, later they sent to SEPTA service in Philadelphia. Still later thdy were sent to Morrison-Knudsen, converted almost back to the original configuration, but without the RPO apartment, and sent to Alaska.

Another New Haven RDC3, the 130, having been converted to a self-propelled tracg inspection car, found itself in the employ of the C&NW. The carbody modifications were numerous. On the right side, the RPO door and window were retained, but the bggage door was filled in using matching flutes below the belt rail, replacing the opposite side's RPO window with stainless sheet above the belt. The second and third passenger windows were removed and and relocated to the left-side in the former location of the baggage door. That displaced door frame was shifted forward to the position of the left side RPO door, which was discarded. On the passenger end, all cab windows, both end and-side, were deepened to within a foot of the floor to provide the observation room. Although the letterboard duplicated the graphics of the original 1950 RDCs, the si[es of the ex-NH 130 featured two sizes of C&NW logos, and the car's front end was painted with green and yellow diagonal stripes.

As built, the RDC3 consisted of a 17 foot Railway Post Office, a 17 foot express room, and a 40 foot, 49-seat passenger section. Some RDC3's were built without RPO apartments, but used an identical carbody to those so equipped. Of the five RDC3's originally owned by the New Haven, #'s 126 and 129 migrated to Pennsylvania DOT ownership, where they were converted to all-coach layout. At first they were assigned to Pittsburgh PAT service, later they sent to SEPTA service in Philadelphia. Still later they were sent to Morrison-Knudsen, converted almost back to the original configuration, but without the RPO apartment, and sent to Alaska. Another New Haven RDC3, the #130, having been converted to a self-propelled track inspection car, found itself in the employ of the C&NW. The carbody modifications were numerous. On the right side, the RPO door and window were retained, but the baggage door was filled in using matching flutes below the belt rail, replacing the opposite side's RPO window with stainless sheet above the belt. The second and third passenger windows were removed and and relocated to the left side in the former location of the baggage door. That displaced door frame was shifted forward to the position of the left side RPO door, which was discarded. On the passenger end, all cab windows, both end and side, were deepened to within a foot of the floor to provide the observation room. Although the letterboard duplicated the graphics of the original 1950 RDCs, the sides of the ex-NH #130 featured two sizes of C&NW logos, and the car's front end was painted with green and yellow diagonal stripes.

Controlling slack and running a smooth train called on the Engineer's skill with both the brake and the throttle. Slowing down for a speed restriction - for example westbound at Western Avenue crossing the Milwaukee Road - the Engineer would set the big brake on the train, but bail off the engine brake, then reduce the throttle to Run 1. He'd release the brake and hit the diamonds right at 30 mph, then get right after the throttle to pull the train out of the restriction smooth and fast, with no slack action. Eastbound, again the Engineer would reduce the throttle to Run 1, but never to Idle. The old F7's and E's would hang on to transition in Run 1. If the Engineer went to Idle and then opened the throttle again, the locomotive power contactors would drop out, then pick up in series, but drop out again because of speed and then pick up in parallel. While all this was going on, the train was just drifting. When the locomotive finally decided to go to work, it gave the train a pretty good boot.

Engineers pride themselves in making smooth stops right on the spot, keeping the passengers - and the conductor - happy. It became a real problem when the C&NW put second-hand E-units from Uncle Pete (Union Pacific) into suburban service. Scoots were all equipped with composition brake shoes - not unlike what you've got on your automobile - cars and locomotives alike. Deceleration was smooth and uniform right down to the final stop. But the Union Pacific locomotives had the old cast iron brake shoes. At speed they felt ineffective, but as the train slowed, those iron shoes would take hold. Very hard. Station stops resembled collisions with a brick wall. Attempts to bail off the engine brake right as the train stopped could not be done consistently. Eastbound trips, run from the cab car, were even worse, since the Engineer could not bail off the engine brake at all. It felt like we'd dropped an anchor on a short chain, and we fully expected to look back and see a cloud of ballast and splintered crossties behind the engine. Since the engine squatted down when it stopped, it would run all the slack out of the train. Starting up again, we could feel the slack come up car by car until it hit the cab car with a good tap. The mechanical people at the diesel ramp (M19A - 40th Street, Chicago) were flooded with complaints, and it wasn't long before those UP engines all had composition brake shoes and new brake cylinders.