The "PIONEER" is an unusual locomotive and on first inspection would seem to be imperfect for service on an American railroad of the 1850's. This locomotive has only one pair of driving wheels and no truck, an arrangement which marks it as very different from the highly successful standard 8-wheel engine of this period. All six wheels of the _Pioneer_ are rigidly attached to the frame. It is only half the size of an 8-wheel engine of 1851 and about the same size of the 4--2--0 so common in this country some 20 years earlier. Its general arrangement is that of the rigid English locomotive which had, years earlier, proven unsuitable for use on U.S. railroads. These objections are more apparent than real, for the _Pioneer_, and other engines of the same design, proved eminently successful when used in the service for which they were built, that of light passenger traffic. The _Pioneer's_ rigid wheelbase is no problem, for when it is compared to that of an 8-wheel engine it is found to be about four feet less; and its small size is no problem when we realize it was not intended for heavy service. Figure 2, a diagram, is a comparison of the _Pioneer_ and a standard 8-wheel locomotive. Since the service life of the _Pioneer_ was spent on the Cumberland Valley Railroad, a brief account of that line is necessary to an understanding of the service history of this locomotive. _Exhibits of the "Pioneer"_ The _Pioneer_ has been a historic relic since 1901. In the fall of that year minor repairs were made to the locomotive so that it might be used in the sesquicentennial celebration at Carlisle, Pennsylvania. On October 22, 1901, the engine was ready for service, but as it neared Carlisle a copper flue burst. The fire was extinguished and the _Pioneer_ was pushed into town by another engine. In the twentieth century, the _Pioneer_ was displayed at the Louisiana Purchase Exposition, St. Louis, Missouri, in 1904, and at the Wheeling, West Virginia, semicentennial in 1913. In 1927 it joined many other historic locomotives at the Baltimore and Ohio Railroad's "Fair of the Iron Horse" which commemorated the first one hundred years of that company. From about 1913 to 1925 the _Pioneer_ also appeared a number of times at the Apple-blossom Festival at Winchester, Virginia. In 1933-1934 it was displayed at the World's Fair in Chicago, and in 1948 at the Railroad Fair in the same city. Between 1934 and March 1947 it was exhibited at the Franklin Institute, Philadelphia, Pennsylvania. The Cumberland Valley Railroad