The Alaska Railroad transported men, materials and supplies via river boats to help construct and maintain the line. In fact, these ships became the railroad's lifeline. However, there were constant battles over freight charges and one company even terminated their river boat service.. In 1923 the Department of the Interior authorized the Alaska Railroad to begin its own operation. They acquired the Gen. Jeff C. Davis and the Gen. J. W. Jacobs via Army surplus. They later acquired the riverboats Alice, Nenana, Yukon and Barry K. The railroad continued this service until 1949.
With the outbreak of World War II and the Aleutian Islands a tempting strategic outpost for Japan, the United States began building army aircraft bases in Fairbanks and Anchorage. The military depended on the Alaska Railroad to transport construction equipment, materials, supplies and men. To help ensure the railroad (and thus the army) could not be shut down by destroying the docks in Seward and to provide another dock to handle the huge amount of military traffic, President Roosevelt authorized the construction of a new route via Whittier. This 12 mile spur would connect with the mainline at Portage (milepost 64.2). Work began in autumn of 1941. Due to severe weather, poor planning and wartime shortages, the line was not completed until the spring of 1943. In June of 1943 the first train rolled out of Whittier, two years after construction began.
Whittier was also the destination of the first diesel engines. Engines #1000 and #1001 made the run on June 15, 1944. These innovative 1,000 horsepower road switching locomotives could be coupled together and operated as a single unit.
The Loop, although an engineering marvel, was a nightmare to maintain. Timbers had to be constantly replaced and the snow fleet had the challenging task of removing snow that got deeper the further they pushed. When more power diesel locomotive technology appeared on the scene, The Loop was replaced in the mid 1950s, thus reducing the extreme maintenance costs to this district.
The streamliner locomotive was another great benefit for the railroad and hailed an eventual end to the steam era.
In 19xx, the first passenger train arrived in McKinley Park, a tradition that continues on even today.
As technology moved forward, better materials became available and railroad bridges were upgraded.