It made for a threatening show of strength against North Korean President Kim Jong-un, and it hasn't gone unnoticed.
With characteristic bravado, North Korea responded with indignant threats. The North's ruling-party published Rodong Sinmun newspaper said: "Any rash military provocation will result in (South Korea) paying a high-price penalty.
"In the past, (South Korea) has been crazy about military provocations driven by a war fever to invade North Korea, but the latest shelling exercise which involved so many artillery units lurking along the front-line is unprecedented."
Long-time allies, the US and South Korea, conduct annual military drills in the region, and have done so for decades.
US officials justify the exercises as solely to ensure readiness for a possible North Korean attack, and suggest that decades of such drills have contributed to stability in Asia.
However, with this year's war games being the largest ever, and with a US decision to deploy a B-1 bomber plane in the Pacific for the first time in a decade, North Korea is claiming that the US's intentions are far from promoting regional stability.
North Korea has accused Washington of planning a pre-emptive nuclear strike.
A North Korean official said: "The enemies are bluffing that they can mount a pre-emptive nuclear strike on the DPRK [North Korea] by letting fly B-1B over the Korean peninsula within two-three hours in contingency.
"Such moves for bolstering nuclear force exposes again that the US imperialists are making a pre-emptive nuclear strike on the DPRK a fait accompli."
Tensions between the West and Pyongyang have been mounting throughout the year, since North Korea resumed its production of plutonium, and carried out its fourth nuclear test in January.
North Korean state media cited the threat of the US increasing its influence in the region as justification.
Last month, US Army Secretary Eric Fanning, acknowledged that despite plans to scale down the size of the US army, the US has increased its presence in Asia-Pacific. The number of soldiers and civilian army workers in the region has risen to more than 100,000, from 70,000, four years ago.
Pyongyang has repeatedly warned it may carry out pre-emptive nuclear strikes against it's southern neighbor, and US bases in the Pacific, if it feels further threatened.
This week's war games are being seen as highly provocative by some regional analysts, in such an atmosphere of mutual mistrust.