A "terrorist hide" was uncovered at Capanagh Forest near Larne after two members of the public found suspicious objects in the woods on Saturday.
Some of the items found included an armour-piercing improvised rocket and two anti-personnel mines.
The main line of police inquiry is the arms belonged to dissident republicans.
Last week, Home Secretary Theresa May said MI5 believed an attack on targets in Great Britain by dissident republicans had become "a strong possibility".
Analysis: Vincent Kearney, BBC News NI's home affairs correspondent
The discovery of what appears to be a second dissident republican arms dump near Larne within three months has left police baffled.
Based on location alone, the analysis would be that the items found most likely belonged to loyalist paramilitaries.
But the nature of what was found suggests otherwise and the finger of suspicion firmly in the direction of dissident republicans.
Det Supt Kevin Geddes said the threat level in Northern Ireland from dissident republican groups remains "severe" and an attack is "highly likely".
Police officers found three barrels hidden in holes in the forest.
As well as rockets and mines, there were also several pipe bombs, assault rifle ammunition and parts to construct a "substantial number of explosive devices".
Det Supt Geddes said the seizure was significant "both in terms of its size and its capability".
"A number of these devices were ready to be deployed," he added.
"This seizure has undoubtedly saved lives."
He said the type of weapons that had been found meant police would focus their investigation on dissident republicans.
In March, an arms find was made at Carnfunnock Country Park near Larne, and police said the were investigating a connection between the two discoveries.
"There are links in terms of the general location and the manner and method of storage and packaging of these munitions," Det Supt Geddes said.
He added that police are "indebted" to the two people who noticed the suspicious objects in the Capanagh Forest.
A discovery of arms in a County Antrim forest was one of the most significant in recent years, police in Northern Ireland have said.