Local health departments typically rely on exercises to test preparedness capacity; however, pre-scripted drills often lack the sense of urgency that a real event would engender. No-notice, unscripted exercises that challenge staff to think critically under pressure may provide a mechanism for a more realistic assessment of preparedness capacity. The very active influenza season of 2012-13 presented the Public Health Preparedness Program at the Philadelphia Department of Public Health with the opportunity to conduct an influenza vaccination clinic at a local boarding school. Program leaders used this opportunity to design a no-notice exercise to test the ability of staff to effectively coordinate an emergency field response while simultaneously delivering a real public health intervention. On the day of the exercise, staff members were given 6 hours to plan and execute a vaccination clinic without any guidance from program leaders. Best practices observed during the exercise included: (1) early identification and mitigation of rate-limiting steps, and (2) successful implementation of a previously untested high-throughput vaccination model. Although the primary intent of the exercise was to assess the ability of staff to respond to a no-notice event, this vaccination clinic also functioned as a microcosm of a larger response, revealing several considerations related to vaccine ordering, staff resources, and throughput rates that have broader implications for public health responses to large-scale biological attacks or pandemics.