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.

Richard Callaghan, of Rathmore Crescent in Creggan, Londonderry, pleaded guilty to being involved in the supply of cocaine and herbal cannabis.
The court heard that police valued the drugs at almost Â£130,000 but the defence said it was half that amount.
The judge sentenced Callaghan to two years and eight months, half of which will be spent on licence.
Almost 0.5kg of cocaine, with a purity level of between 12% and 13%, and 5kg of herbal cannabis were found in a wheelie bin at the back of a car driven by Callaghan at Beechwood Crescent in Derry on 13 June last year.
Police officers saw Callaghan, along with another man who ran off, lifting out the spare wheel of the car and loading the drugs from the boot into the bin.
The car used in the drugs run was bought by another man on the internet and given to Callaghan in return for him driving the drugs to Beechwood Crescent.
Callaghan drove the car from a garage in County Armagh where the drugs had been loaded into the vehicle.
On his way to Derry, he stopped to check on the consignment of drugs.
The judge at Londonderry Crown Court described Callaghan as an active courier, and said whatever the value of the drugs it was still a significant amount.
He said Callaghan got involved in what he called "this crazy scheme" because he was in debt due to his own cannabis habit.
PSNI Det Insp Tom McClure said the sentence was "the result of a substantial proactive investigation".
"The message from this sentence is clear: all those involved in the supply chain of large quantities of controlled drugs can expect to go to prison when they are caught.
"Police will work to ensure Northern Ireland remains a hostile environment for those who seek to benefit in any way from peddling the misery of drugs."
A discovery of arms in a County Antrim forest was one of the most significant in recent years, police in Northern Ireland have said.
[NEXT_CONCEPT]
A man who was caught in a police anti-drugs operation last year has been jailed.