Auto loan growth at Navy Federal Credit Union was up 36% as of June, more than double the national average of 14%.

The $49 billion credit union in Vienna, Va., said a yearlong membership surge has helped the cooperative grow its auto loan portfolio. Low rates and its capacity to serve members quickly, especially among those seeking deals on new cars, have also contributed to loan growth, Navy Federal said.

Since September 2011, when the credit union’s auto rates dropped to their lowest, more than 350,000 new members joined, spurring consecutive monthly auto loan growth, according to the credit union.

In July alone, Navy Federal was able to put about 24,000 members in cars, said Tony Gallardy, vice president of consumer lending.

Earlier this year, Callahan & Associates named Navy Federal among the top credit union auto lenders in the country.

The credit union said it is also seeing an outperforming of new car loans over used cars by 45%. This trend is also a departure from the national norm, Navy Federal said.

Members also like the quick turnaround. According to the credit union, either online, by phone, or in the branch, the turnaround from loan application to approval is many times less than 15 minutes.

Navy Federal said it now serves 4 million members and has 222 branches and more than 9,000 employees worldwide.