Thank you, Steve.
Continued strong demand in our markets has driven outstanding lease achievement this year.
Third quarter vacancy leasing was exceptionally strong at 215,000 square feet representing 18% of our available space at the beginning of the quarter. To put this achievement in perspective, since defense spending began rebounding in 2016, our quarterly vacancy leasing has averaged 132,000 square feet. There were two major transactions from the quarter worth highlighting.
The first of which was a 68,000 square foot lease with the U.S. government at 310 NBP, leaving two floors to lease to bring that building to 100%. The customer continues to indicate their intent to lease the remaining space, but because the government is operating under a continuing resolution, we now project lease execution during 2022.
The second major vacancy lease was for 63,000 square feet at 6740 Alexander Bell Drive in Columbia Gateway. The new tenant is consolidating multiple offices and executed a 16.5-year lease for the entire building with lease commencement expected in July 2022.
Although, we had intended to redevelop this asset, we backfilled the full building in just four months and accordingly have moved it back into our same property pool.
For the nine months, our 420,000 square feet of vacancy leasing represented 114% of the trailing five-year average through nine months and with the second highest nine-month volume in the past five years.
Our current leasing activity ratio is 101% and since the start of the second quarter has averaged 90% underpinning much of the third quarter's vacancy leasing success and our expectation for strong lease achievements continuing into the fourth quarter.
During the third quarter, we renewed 553,000 square feet translating into a 76% tenant retention rate. Cash rents and renewals rolled it down six-tenths of a percent and gap rents grew 1%.
Excluding an 89,000 square foot renewal where the tenant was rolling off a 10-year lease that had escalated above market cash and gap rents increased 1% and 5% respectively in the quarter.
For the nine-month period, we completed 1.4 million square feet of renewals with a 75% retention rate, cash rents rolling down three-tenths of a percent with annual escalations averaging 2.4%, and average initial lease terms of 3.8 years.
Excluding the two Boeing buildings in Redstone Gateway that are still on one-year renewals, the lease term for the nine months averaged 4.7 years.
We continue to advance negotiations to renew the 11.25 megawatt user at DC6. The customers' process remain slow and methodical and we are confident they will renew, given we cannot control their pace; we are not putting a timeframe on its completion. The tenant's original lease remains in effect and they continue to pay their escalated rent.
During the quarter, we executed 274,000 square feet of development leasing at Redstone Gateway. The largest transaction was a 205,000 square foot full building lease with the U.S. government. Lease commencement is scheduled for early 2024. This development represents our second building in the secured campus, which upon completion of this project will total 460,000 square feet. The remaining 69,000 square feet of development leasing was with two defense contractors who leased space at 8000 Rideout Road. That development was started because of the contractor demand we are tracking and is now 88% leased.
We are working to close a lease for the remaining 12,000 square feet. Earlier this month, we executed leases with Northrop Grumman for two build-to-suite office buildings along Rideout Road at Redstone Gateway. The two building campus totals 263,000 square feet of highly visible Class A office space with one of the world's largest defense contractors, just outside Redstone Arsenal's main gate.
We are on track for lease commencement in the second half of next year. Once the active projects under development at Redstone Gateway are placed into service, the park will total 2.2 million square feet making it our second largest concentration of defense IT assets and equal to slightly more than half the size of the National Business Park. The Northrop leases brought our year-to-date development leasing total to nearly 1.2 million square feet, making 2021 the 10th straight year, we have exceeded our development leasing goal. Based on the 1.5 million square feet of opportunities, we are tracking in our development leasing pipeline; we expect continued strong development leasing.
Lastly, in the first nine months, we've raised 709,000 square feet of developments into service that were 89% leased.
We expect to place another 74,000 square feet into service in the fourth quarter bringing our total for the year to roughly 800,000 square feet. With that, I'll turn the call over to Anthony.