Which Apollo mission placed the first seismometer on the Moon?

Apollo 11 placed the first seismometer on the Moon.

Neil Armstrong and Buzz Aldrin deployed the Early Apollo Scientific Experiment Package near the lunar module Eagle in July 1969. Its passive seismic experiment detected vibrations in the lunar ground, helping scientists study the Moon’s internal structure and natural activity.

The instrument was part of Apollo 11’s small group of scientific experiments, which also included a laser-ranging retroreflector and a solar-wind experiment. Later Apollo missions delivered more capable seismometers and expanded the lunar geophysical network.

A common mix-up is to credit Apollo 12 with the first seismometer because that mission deployed a more extensive scientific station. Apollo 11 nevertheless made the first lunar seismic measurements with its instrument.