Question: How many acres were purchased in Plymouth County, Massachusetts in 1918 for a proving ground operation?

Context articles: Scituate Proving Ground
Southwestern Proving Ground Building No. 5
Sandy Hook Proving Ground
Plymouth North High School
Southwestern Proving Ground Building No. 129
Plymouth County Correctional Facility
Erie Proving Ground
Scituate, Massachusetts
Plymouth County, Iowa
Brockton, Massachusetts

Scituate Proving Ground was a proving ground of the United States Army located in Scituate, Massachusetts.
 It was operational from 1918 when 115.25 acres were purchased between June and July.
 In November 1919, the site was declared excess, and it was used as a storing ground until June 1921.
 Today, the site is used for housing, although former structures dating from the use of the grounds still can be seen.
The Southwestern Proving Ground Building No. 5 is an ammunition storage bunker at 259 Hempstead County Road 279 in Oakhaven, Arkansas, northwest of the city of Hope.
 It is located on property that was once part of the Southwestern Proving Ground, a major military facility during World War II whose largest portion was transformed into Hope Municipal Airport.
 Building No. 5 is a single-story concrete structure with a rounded roof, covered in earth, and with a heavy steel door facing northwest.
 It is one of three ammunition bunkers built on the proving ground (the others, Building Nos. 32 and 33, also survive).
 The building is used as storage by a private owner.
The Sandy Hook Proving Ground was a military facility along the Atlantic coast of New Jersey established by the Secretary of War on August 7, 1874, to serve as the United States Army's first proving ground for the testing of ordnance and materiel.
 The facility was located at Sandy Hook, a narrow coastal spit of land, approximately 6 mi in length and 0.5 miles (varying between 0.1 and 1 miles) wide, in Middletown Township in Monmouth County.
 The facility was operated in conjunction with the adjoining Fort Hancock.
 Essentially abandoned in 1919 for a larger facility, the area was left to degrade and most of the structures still remain today.
 The proving ground and parts of Fort Hancock are now property of the National Park Service and mostly closed to the public.
Plymouth North High School, known informally as Plymouth North or PNHS, is a public high school located in Plymouth, Massachusetts.
 Its students are residents of the town of Plymouth.
 The school is one of two high schools in Plymouth, the other being Plymouth South High School.
 Plymouth North is located south of Plymouth Center, and is located adjacent to the Plymouth County Courthouse, the Plymouth County Registry of Deeds, and Beth Israel Deaconess Hospital.
 The school currently has an enrollment of 1054 students, in grades 9–12.
 The school colors are Navy Blue, White & Silver and the school mascot is an Eagle.
The Southwestern Proving Ground Building No. 129 is a military powder magazine at 195 Hempstead County Road 279 in Oakhaven, Arkansas, northwest of the city of Hope.
 It is located on property that was once part of the Southwestern Proving Ground, a major military facility during World War II whose largest portion was transformed into Hope Municipal Airport.
 Building No. 129 is a single-story brick and tile structure, with two bays.
 There are red steel doors located on the northeast and southwest facades.
 The roof is gabled, and covered in fire-resistant asbestos sheeting, with vents at the ridge, and an elaborate lightning-protection system.
 It was built in 1941 to house smokeless gunpowder, and is one of only two brick buildings from the proving ground to survive.
 It is now used by a private owner for storage.
Plymouth County Correctional Facility is a maximum-security prison located in Plymouth, Massachusetts Operated by the Plymouth County Sheriff's Department.
 The prison is the largest prison in Plymouth, and is much larger than the Massachusetts Correctional Institution - Plymouth, located in the Myles Standish State Forest.
 The prison is known for housing several celebrity inmates, most notably "" winner Richard Hatch, shoe-bomber Richard Reid, former President of Liberia Charles Taylor, reputed Boston mob boss James "Whitey" Bulger, as well as multiple murderer Gary Sampson, and former New England crime boss Francis "Cadillac Frank" Salemme.
Erie Proving Ground was a former United States Army facility.
 Originally a camp to train gunners, the facility's foundation was due to the Spanish–American War's lack of skilled riflemen.
 The facility was located in Ottawa County, Ohio.
 The facility was established in 1918 originally as Camp Perry Proving Ground.
 The facility was at various times named Erie Ordnance Depot and Erie Army Depot.
 During World War II over 5,000 people ended up being employed there.
 The employed people were testing various weapon systems, armor, and such during World War II.
 During peacetime it served as a storage, maintenance, and repair facility.
 Erie Proving Ground closed in January 1967.
Scituate ( ) is a seacoast town in Plymouth County, Massachusetts, United States, on the South Shore, midway between Boston and Plymouth.
 The population was 18,133 at the 2010 census.
Plymouth County is a county located in the U.S. state of Iowa.
 As of the 2010 census, the population was 24,986.
 The county seat is Le Mars.
 Plymouth County was named after Plymouth, Massachusetts.
Brockton is a city in Plymouth County, Massachusetts, United States; the population was 95,314 in the 2015 Census.
 Brockton, along with Plymouth, are the county seats of Plymouth County.
 Brockton is the seventh largest city in Massachusetts and is sometimes referred to as the "City of Champions", due to the success of native boxers Rocky Marciano and Marvin Hagler, as well as its successful Brockton High School sports programs.
 Two of the villages within the city are Montello and Campello, both have the distinction of having their own MBTA Commuter Rail Stations and post offices.
 Campello is the smallest neighborhood in the city, but also the most populous.
 Brockton hosts a baseball team, the Brockton Rox.
 Brockton is one of the windiest cities in the United States, with an average wind speed of 14.3 mph.