6- I’m more familiar with the LGA<>DCA shuttle, but I have to believe the BOS logic was similar (notwithstanding DCA peculiarities like jet curfews)

• Eastern started the on-the-hour Air-Shuttle service in both markets in the early 1960s, mainly using Lockheed Electras; the “guaranteed seat” concept meant that you could show up at the gate at 0957, and if the scheduled 1000 departure was already full, they would bring another plane over *just for you* (many of the backup sections were actually operated with Lockheed L-1049C/G Super Constellations)
• when DCA opened to jet operations in Apr 1966, EA switched the primary Shuttle fleet to the DC-9-30, but maintained both Electras and Connies as backup equipment for several more years (the last LGA-DCA flight and the first DCA-LGA used Electras due to the aforementioned jet curfews)
• American entered the LGA-DCA/BOS market around that time with BAC 1-11-400 flights, but iirc didn’t actually operate these as a “Shuttle” service
• by the mid 1970s EA had upgauged most of the Shuttle operations to the 727-200, and AA was down to a handful of flights with 727/72S equipment on each route
• New York Air showed up in both markets with hourly D9S service in the early 1980s; EA responded by upgauging LGA<>BOS to A300s
• by 1989 the competition was Pan Am vs Trump Shuttle, both airlines using the 72S; Delta acquired PA in early 1991 and maintained both Shuttle operations, and USAir acquired TS the following year
• I flew both DL Shuttle routes on 737-300s (2004) and MD-80s (2007)
• not exactly sure of the timeframe (2010-2015?), but DL migrated most of the Shuttle routes to regional affiliates (Republic, Endeavor, others?) with ERJ-170/175 aircraft
• in the same timeframe, US used a mix of A319s and EMB-190s, and JetBlue operated A320s and E90s
• AA maintained most of the US operations after the merger, but retired the E90 fleet ~2018