tunnel from Fourth Street to 53rd Street. Part of this stretch was already occupied by the Hudson & Manhattan Railroad (H&M)'s Uptown Hudson Tubes. As a result, negotiations between the city and the H&M continued for several years. The IND and H&M finally came to an agreement in 1930. The city had decided to build the IND Sixth Avenue Line's local tracks around the pre-existing H&M tubes, and add express tracks for the IND underneath the H&M tubes at a later date. Also in 1930, the BOT identified the locations of 104 stations to be built in the IND system. Under this plan, there would have been an express station at Sixth Avenue and 50th Street. The IND started advertising bids for the section of the Sixth Avenue Line between 43rd and 53rd Streets in April 1931. In April 1935, engineers started planning in earnest for the Midtown portion of the Sixth Avenue Line. The city government issued corporate stock to pay for the $53 million cost of the project, since the line was not eligible for federal Public Works Administration funds. The first contract, for the section between 40th and 47th Streets (just south of the Rockefeller Center station), was awarded to Rosoff-Brader Construction in October 1935. Mayor Fiorello H. La Guardia broke ground for the Sixth Avenue subway at Bryant Park on March 23, 1936. As part of the first phase of the project, the contractors built a compressor plant and a shaft at 46th Street. In November 1936, the George A. Flynn Corporation received a $4,616,476 contract for the construction of the section between 47th and 53rd Streets. The line was built as a four-track tunnel north of 33rd Street (including the Rockefeller Center station), but there were only two tracks south of that street. The work largely involved cut-and-cover excavations, although portions of the subway had to be tunneled through solid rock. The builders also had to avoid disrupting the Sixth Avenue elevated or the various utility lines on the avenue, and some of the utility pipes and wires under Sixth Avenue had to be replaced in the process. Excavation work was conducted 24 hours a day, with most of the blasting work being conducted at night. Workers used small charges of dynamite to avoid damaging nearby buildings or the Catskill Aqueduct, which ran below Sixth Avenue and was a major part of the New York