The defenses of Cork Harbour faced two threats.
Firstly an attack by war-ships forcing entry into the harbour - either in a raid to destroy shipping or to effect a landing of troops.
Secondly they faced the threat of attack from the land by forces which had been landed at an undefended point along the coast.
Just such a landing had been attempted by the French at Bantry Bay in 1796 with a force of fifteen thousand men.
While unsuccessful, the attempt greatly alarmed the military.
Vallancey was of the belief that had the French actually landed, they would have taken the Cork Harbour forts, including Fort Westmorland.

In 1802, General John Hope, 4th Earl of Hopetoun, recommended that a major fortress is constructed on Spike Island, capable of holding 2,000-3,000 men.
He considered Spike Island was for Cork Harbour 'the true point of defence' Lieutenant General David Dundas was consulted by the Duke of York, Commander in Chief, who also recommended that a fortress should be erected on Spike Island.
Wiliam Twiss of the Royal Engineers concurred.

In 1801 The Acts of Union came into force and responsibility for fortifications in Ireland passed from the Irish Board of Ordnance, which was abolished, to the Board of Ordnance in London.
It was the job of the Board to implement the decision to erect the fortress and it fell to Charles Holloway Commanding Engineer Cork District to begin the works.
In 1804 The Hampshire Chronicle reported that the overall height of Spike island had been reduced by 25 feet and the spoil used as infill to create a level foundation.
The same paper reported that on 6 June 1804 General Sir Eyre Coote had laid the foundation stone of the new fortress.
 
Two alternative proposals had been made for accommodation within the fort.
One envisaged six barrack blocks, one of which was actually constructed in the fort, this being the officers mess block, The ground floor of these blocks consisted of a series of bombproof brick vaulted rooms.
The first floor was slate-roofed and open to destruction in the event of a bombardment.
The second proposal was for 6 sets of bombproof casemates set into the ramparts.
Two such sets of casemates were actually constructed, these being the north-east and north-west casemates.
The second accommodation block to be constructed, the A Block, shows a divergence from the original plan in that the bombproofing is incorporated into the roof.
The ground floor of a third block, the B Block, was intended to follow the design of the A block, was erected before the first phase of construction ended (circa 1817).
The four magazines were also constructed around this time.
A large workforce was employed in the construction, and included both troops and civilian workmen.
The defenses of Cork Harbour faced two threats. Firstly an attack by war-ships forcing entry into the harbour - either in a raid to destroy shipping or to effect a landing of troops. Secondly they faced the threat of attack from the land by forces which had been landed at an undefended point along the coast. Just such a landing had been attempted by the French at Bantry Bay in 1796 with a force of fifteen thousand men. While unsuccessful, the attempt greatly alarmed the military. Vallancey was of the belief that had the French actually landed, they would have taken the Cork Harbour forts, including Fort Westmorland.
In 1802, General John Hope, 4th Earl of Hopetoun, recommended that a major fortress is constructed on Spike Island, capable of holding 2,000-3,000 men. He considered Spike Island was for Cork Harbour 'the true point of defence' Lieutenant General David Dundas was consulted by the Duke of York, Commander in Chief, who also recommended that a fortress should be erected on Spike Island. Wiliam Twiss of the Royal Engineers concurred.
In 1801 The Acts of Union came into force and responsibility for fortifications in Ireland passed from the Irish Board of Ordnance, which was abolished, to the Board of Ordnance in London. It was the job of the Board to implement the decision to erect the fortress and it fell to Charles Holloway Commanding Engineer Cork District to begin the works. In 1804 The Hampshire Chronicle reported that the overall height of Spike island had been reduced by 25 feet and the spoil used as infill to create a level foundation. The same paper reported that on 6 June 1804 General Sir Eyre Coote had laid the foundation stone of the new fortress.  
Two alternative proposals had been made for accommodation within the fort. One envisaged six barrack blocks, one of which was actually constructed in the fort, this being the officers mess block, The ground floor of these blocks consisted of a series of bombproof brick vaulted rooms. The first floor was slate-roofed and open to destruction in the event of a bombardment. The second proposal was for 6 sets of bombproof casemates set into the ramparts. Two such sets of casemates were actually constructed, these being the north-east and north-west casemates. The second accommodation block to be constructed, the A Block, shows a divergence from the original plan in that the bombproofing is incorporated into the roof. The ground floor of a third block, the B Block, was intended to follow the design of the A block, was erected before the first phase of construction ended (circa 1817). The four magazines were also constructed around this time. A large workforce was employed in the construction, and included both troops and civilian workmen.
Spike Island, County Cork