In 1873 at the beginning of the Endicott Period forty acres of land was acquired on Gerrish Island and work began on Battery Berry, named after Major General Heiram G. Berry, a wide V shaped twelve gun earthwork and concrete battery that was intended to be armed with 15" Rodman M1861 Columbiads with 190" barrels in double bays with transverse magazines on wrought iron barbette carriages. Apparently only the parapet, gun platforms and two transverse magazines of the battery were ever completed and the battery was never actually armed. Battery Berry was demolished in 1898 and there are no known remains.
In 1898 construction was started on Battery Henry Bohlen, named after Brigadier General Henry Bohlen, at the site where Battery Berry had been built and the construction was finished in 1901. The two story concrete battery with earth embankments had the loading platforms, gun decks and four crows nests on the second floor and was armed with three 10" 35 caliber M1895 breach loading rifles with 369.15" barrels on M1896 disappearing carriages. The first floor had three magazines, two shell rooms and numerous other rooms. Two Hodges back-delivery projectile hoists were installed to bring the shells up from the first level. On August 17, 1917 orders were received to remove the guns from the battery and send them to the Aberdeen Proving Grounds so they could be sent to France, which was done on October 2, 1917. The guns were returned to Fort Foster on October 10, 1919 and were remounted on the battery. In 1921 a back-up fire-control station was built slightly short of a mile away from the battery on Sewards Point. Constructed of reinforced concrete, the station had three five foot walls with an open top and a concrete instrument panel. In 1922 the Hodges hoists were removed and three GE Taylor-Raymond back-delivery projectile hoists were installed in the battery. On December 15, 1942 the battery was deactivated and the guns were removed and sent off to be salvaged. The battery still exists, however the first level has been filled in with sand so only the upper level and crows nests remain open to the public. The back-up fire-control station still exists but it is on private property and there is no public admittance.
In 1900 the emerging fort was named Fort Foster, after Major General John G. Foster, and it was made a sub-post of Fort Constitution. In 1903 construction was started on Battery Edward Chapin, named after Brigadier General Edward P. Chapin, a two story concrete structure. The first floor had from left to right a magazine, a storeroom and another magazine all accessible from doors in the back of the battery. The second floor had the gun decks. The battery was finished on December 31, 1904 and the battery was armed with two 3" M1902MI shielded rapid-fire rifles with 154.35" barrels on M1902 pedestal mounts. The shells had to be carried up to the second story from the first story. In 1920 a CRF (Coincidence Rangefinder) station was built on top of Battery Chapin. On October 18, 1945 Battery Chapin was deactivated and the guns were removed and sent off to be salvaged. The battery still exists today and is open for public admittance.
In 1908 the U.S. Lifesaving Service built a two story wood frame and masonry building with a wooden four story observation tower that became the Portsmouth Harbor Lifesaving Station and a tool shed on Wood Island just off Fort Foster. The building contained officer's and crew's quarters, bathrooms, a boat house, a basement, living room, mess hall, kitchen, station chief's office, equipment storage and an exterior observation deck on the fourth floor of the tower. The crew and equipment from Jerry's Point Lifesaving Station at Fort Stark were transferred to the new station. In 1915 the U.S. Lifesaving Service became the U.S. Coast Guard. In 1941 the U.S. Navy took possession of Wood Island and used the building as an observation station for Portsmouth Harbor and anchored the harbor submarine net to the island. In 1945 the island was transferred back to the U.S. Coast Guard who used it until they moved to Fort Constitution in 1948. The station and tool shed still exist today but both are badly decayed and falling down. Cribworks from the submarine net can still be seen stretching from Fort Foster to Wood Island.
In 1909 a two story tower like wooden Mine Observation Station with a concrete instrument panel with a depression rangefinder instrument on top was constructed behind Battery Chapin. The upper story held an observation room. The mine observation station was a back-up station for the primary Mine Observation Station located at Fort Stark. A quartermaster's wharf and an NCO/caretaker dwelling were also built on the fort. The concrete instrument panel for the Mine Observation Station still exists. No other buildings from this period remain. In 1915 temporary officers quarters, temporary barracks, a temporary post exchange, a temporary stable, a permanent garage and permanent engineer storehouse were built in the fort. In 1920, two truck mounted 60" Sperry searchlights (positions 6 and 7) were emplaced on Sewards Point near the back-up fire-control station for Battery Bohlen. When they weren't in use they were stored at Fort Foster. The seachlights were removed and shipped to Fort Totten in 1921. In 1922 a reinforced concrete single room searchlight shelter was built next to Battery Bohlen that held a rail mounted 60" Sperry searchlight (position 5 for WWI and position 12 for WWII). All of the temporary buildings were removed in the 1920s. In the 1930s NC officers quarters were built. The searchlight shelter still exists but no other buildings do.
In August of 1941 land was purchased on Sisters Point and in 1942 the Sisters Point Base-End Station (location 149), a five story square reinforced concrete tower, was completed. The third floor was for Battery Seaman at Fort Dearborn (station designation B9/2 S9/2), the fourth floor was for Battery Barry at Fort Dearborn (station designation B5/1 S5/1), the fifth floor was going to be used for Battery Curtis at Fort Foster (station designation B4/6 S4/6) and the roof was used for anti-aircraft purposes (station designation AAIS OP 8). Battery Curtis was never activated so Harbor Defense Operations took over the fifth floor (station designation HD OPS 3). Barracks, an SCR-296A fire control radar on a 100 foot steel frame tower and a concrete block operating room were also built at this location. There were also two 60" Sperry searchlights (positions 13 and 14). The Sisters Point encampment was not directly under the command of Fort Foster but instead fell under the command of the HECP at Fort Stark. The concrete tower was destroyed in 2004 and no remains of any of the other buildings still exist.
On January 15, 1942 forty eight more acres of land was purchased and on November 10, 1942 construction was started on Battery 205 (location 148 site 1A) also known as Battery Curtis, named after Major Edwin S. Curtis. The battery was going to have two 6" rapid-fire T2-M1 rifles with 309.9" barrels on M4 shielded barbette carriages. On September 8, 1944 the earth covered single story reinforced concrete casemated battery was completed with the carriages installed. The battery was 144 feet by 99 feet and 44 feet high. The main corridor had two store rooms, two powder rooms, six shell rooms, an air compressor generator room, an air compressor and motor service room and another corridor at a 90 degree angle. Down the other corridor are the power room, muffler galley, water cooler room, plotting room, switchboard, spotting and radio room and the service core with latrine. The battery was decommissioned in 1944 so the T2-M1 rifles were never installed on the carriages and the battery was never activated. Two 50 caliber drum-fed heavy machine guns and two automatic 40mm mobile AA guns Model M2 with 87" barrels were also installed on the battery. On May 19, 1943 construction was finished on a six story square reinforced concrete tower that was to serve as the Battery Commander's Station and Operations for Battery Curtis. The fifth floor was the battery command post and the sixth floor was the operations post. Battery Curtis still exists but the doors are sealed and there is no public admittance and the tower still exists but the doors are sealed and there is no public admittance.
On July 8, 1942 a three story reinforced concrete mine observation station was finished by Battery Bohlen. The second floor served as a plotting room and the third floor held a double observation station. One side was for the Mine Group Commander (station designation MG OP 1) and the other side was for the M2 Mine Group, which handled the outer two mine lines and served as a back-up for the Mine Observation Station at Fort Constitution. A new earth covered reinforced concrete mine casemate was built by Battery Bohlen in 1942 as well. It handled firing the outer two mine lines of the three line mine net across the harbor. It also served as a back-up for the mine casemate located at Fort Constitution. Fort Constitution's mine casemate also served as the back-up for Fort Foster. Sixty six man barracks, a mess hall, an administration building, an infirmary, two recreation buildings, six man officer's quarters/mess and a one story wooden battery commander's station were also built. The submarine net was anchored to Fort Foster and stretched to Wood Island and then from Wood Island stretched to the harbor side of Fort Stark. The mine casemate still exists today but is sealed to the public. The mine observation station still exists as well. The bottom floor has been converted into restrooms and the upper floors are sealed off. The submarine net cribworks are still stretched between Fort Foster and Wood Island.
Also in 1942 AMTB Battery 352 was set-up around Battery Barry consisting of two mobile 37mm AA guns with 82.68" barrels on M3 mounts. The two 37mm guns of Battery 352 were replaced with two mobile 40mm M1 Bofors AA guns with 87" barrels on M3 mounts. The ammunition for the battery was kept at the now deactivated Battery Bohlen. Battery 352 was deactivated in 1946.
Built in 1943 next to Battery Bohlen was AMTB Battery 952 consisting of two shielded 90mm M1 rapid-fire guns with 181.10" barrels on fixed M3 mounts on circular reinforced concrete pads. Four drum-fed 50 caliber heavy machine guns and two mobile 90mm M1 rapid-fire guns with 181.10" barrels on M1A1 mounts were also part of the battery. Two earth covered concrete magazines were also constructed. The ammunition for the battery was stored at the now deactivated Battery Bohlen. Battery 952 was deactivated in 1946. One of the concrete mounts still exists under a gazebo. In 1944 a mobile SCR-268 searchlight, AA fire-control and early warning radar was installed at the camp on Sisters Point.
In 1948 Fort Foster was deactivated and the remaining guns were removed and sent to be scrapped. The land was transferred to the town of Kittery, Maine for use as a town park.