From 1900 until 1946, the PV&T and NYNH&H ran joint passenger trains from New York to Portland. As time passed, both the railroads electrified parts of their mainline, and by 1928 the joint trains needed three engine changes; from electric to steam in New Haven, and then from steam back to electric in New London.

At first, the PV&T thought the New Haven would finish their electrification to Boston, and ordered a prototype class C dual-voltage locomotive, with the plan of getting 10 or so of them to allow runthrough passenger trains from Portland to NYC and Montreal to NYC.

And then the US economy crashed, as did any hope that the New Haven would finish their electrification, so that plan came to an abrupt stop. But despite the depression, both railroads still kept the Portland to NYC trains running, and when the New Haven started assembling their new fleet of ALCO DL109s the PV&T put in a piggyback order for a pair of them as well.

The pair was delivered in 1941, and were put into operation pulling passenger trains from New Haven to Concord, mingling with some of the last steam engines on the Parsons Vale, and were worked into the ground as pooled power with the New Haven, at least until the end of WW2 when passenger numbers evaporated.

In 1946, the joint trains stopped running and the DL1s were leased to the LT&L for passenger service along the St Lawrence and down to Bangor on the old B&Q, which they continued doing until VIA Rail took over passenger service in 1977.

A third DL109 joined the small fleet in 1971: one of the New Haven DL109s had been converted to a power test unit for the (failed) Roger Williams trainsets, and had spent about 10 years rotting away in the New Haven’s Boston yards before Penn Central absorbed the New Haven; when PC decided to clean out the yard & scrap the junk engines that were dumped there, workers at the TdM shops bought the carcass, brought it up to Iberville, did a major rebuild, and put it into service on the LT&L as a freight unit (to be joined by the other two in 1977 after their passenger service was done.)