Though originally planned to use high-floor rapid transit trains, the East Boston Tunnel opened with streetcars serving low-platform stations.
Large bi-loading streetcars (with high floors but capable of loading from low platforms), which incorporated many attributes from metro cars used on the Main Line El, began use in 1905.
However, neither these nor the large center-entrance cars introduced in 1917 (which were designed for multiple unit operation) could fully handle the crowds.

In 1921, the Boston Transit Department (BTD)—the successor to the BTC—began work at Maverick Square to convert the East Boston Tunnel to high-floor metro trains.
The next year, the BTD board approved the construction of high-level platforms at Atlantic Avenue, Devonshire, Scollay Under, and Bowdoin.
Construction of concrete high-level platforms 40 inches (1.0 m) above the rails at Bowdoin began in December 1923 or January 1924.
A section of low-level platform was left to serve streetcars during construction.
Temporary wooden platform sections were put in place to allow service to begin on April 21, with the permanent concrete sections completed by July 12.
The Bowdoin platform was also extended 28 feet (8.5 m) east from August 27 to December 12.

Rather than modify the tunnel, the BERy elected to build smaller-than-usual rapid transit cars which could operate in a tunnel designed for streetcars—particularly around the tight loop at Bowdoin.
Blue Line cars are thus 48.5 feet (14.8 m) long, substantially shorter than the 65-foot (20 m) Orange Line cars and the 69.5-foot (21.2 m) Red Line cars.
Because the line did not have a dedicated heavy maintenance facility, major repair work was performed at Eliot Shops – the main maintenance facility for the Cambridge–Dorchester Line.
Trains used the former streetcar portal west of Bowdoin and ran on surface streetcar tracks on the Longfellow Bridge, which connected to the Cambridge–Dorchester Line tracks near Kendall Square.
When the first phase of the Revere Extension opened to Orient Heights with a new maintenance facility in 1952, the connection was no longer necessary and the portal was filled.

The newly-formed Massachusetts Bay Transportation Authority (MBTA) assigned colors to the four MBTA subway lines in 1965, with the East Boston Tunnel and Revere Extension becoming the Blue Line.
The station was modernized in 1968 as part of a $9 million systemwide station improvement program.
The original entrances at the west end of the station were replaced with a glassy entrance under a tilted concrete slab, set into a shallow depression to reduce the costs of installing the escalator.
The new brutalist headhouse, near the middle of the station, was designed by Josep Lluís Sert as part of a project for a never-built Catholic chapel nearby.
Illustrations showing the history of Bowdoin Square were added to the station signs.
The station was surveyed in 1984 and 1987 for potential inclusion on the National Register of Historic Places; it was concluded that the 1924 and 1968 reconstructions had left little of the original station, and that it was of minor significance within the system.
Though originally planned to use high-floor rapid transit trains, the East Boston Tunnel opened with streetcars serving low-platform stations. Large bi-loading streetcars (with high floors but capable of loading from low platforms), which incorporated many attributes from metro cars used on the Main Line El, began use in 1905. However, neither these nor the large center-entrance cars introduced in 1917 (which were designed for multiple unit operation) could fully handle the crowds.
In 1921, the Boston Transit Department (BTD)—the successor to the BTC—began work at Maverick Square to convert the East Boston Tunnel to high-floor metro trains. The next year, the BTD board approved the construction of high-level platforms at Atlantic Avenue, Devonshire, Scollay Under, and Bowdoin. Construction of concrete high-level platforms 40 inches (1.0 m) above the rails at Bowdoin began in December 1923 or January 1924. A section of low-level platform was left to serve streetcars during construction. Temporary wooden platform sections were put in place to allow service to begin on April 21, with the permanent concrete sections completed by July 12. The Bowdoin platform was also extended 28 feet (8.5 m) east from August 27 to December 12.
Rather than modify the tunnel, the BERy elected to build smaller-than-usual rapid transit cars which could operate in a tunnel designed for streetcars—particularly around the tight loop at Bowdoin. Blue Line cars are thus 48.5 feet (14.8 m) long, substantially shorter than the 65-foot (20 m) Orange Line cars and the 69.5-foot (21.2 m) Red Line cars. Because the line did not have a dedicated heavy maintenance facility, major repair work was performed at Eliot Shops – the main maintenance facility for the Cambridge–Dorchester Line. Trains used the former streetcar portal west of Bowdoin and ran on surface streetcar tracks on the Longfellow Bridge, which connected to the Cambridge–Dorchester Line tracks near Kendall Square. When the first phase of the Revere Extension opened to Orient Heights with a new maintenance facility in 1952, the connection was no longer necessary and the portal was filled.
The newly-formed Massachusetts Bay Transportation Authority (MBTA) assigned colors to the four MBTA subway lines in 1965, with the East Boston Tunnel and Revere Extension becoming the Blue Line. The station was modernized in 1968 as part of a $9 million systemwide station improvement program. The original entrances at the west end of the station were replaced with a glassy entrance under a tilted concrete slab, set into a shallow depression to reduce the costs of installing the escalator. The new brutalist headhouse, near the middle of the station, was designed by Josep Lluís Sert as part of a project for a never-built Catholic chapel nearby. Illustrations showing the history of Bowdoin Square were added to the station signs. The station was surveyed in 1984 and 1987 for potential inclusion on the National Register of Historic Places; it was concluded that the 1924 and 1968 reconstructions had left little of the original station, and that it was of minor significance within the system.
Bowdoin station