In Oct, 2014, installation of the largest North American scientific cabled observatory was completed. The Cabled Array portion of the Ocean Observatories Initiative, funded by the U.S. National Science Foundation and implemented by the University of Washington, consists of over 850 km of fiber optic and electrical cables, 7 primary nodes, 18 seafloor junction boxes, 3 mooring-mounted winched profiling systems, 3 rechargeable wire-crawling profiler systems and 140 science instruments. The primary nodes and backbone cables, installed using standard telecommunications industry practices and designed to last a quarter century, bring unprecedented power and bandwidth to remote seafloor locations. Meanwhile, the modular, ROV-serviceable secondary infrastructure branches power and communications in support of instrumentation throughout the water column. The modular design of the secondary infrastructure provides the capacity to expand the cabled network well beyond its initial footprint. To facilitate full shore-based operations, a suite of management software was developed for network configuration, power control, port monitoring, system condition monitoring, configuring alarms, and troubleshooting. These systems are part of a growing new trend of real-time remote ocean monitoring, or interactive observatory-class, systems. The purpose-built observatory-class systems for the OOI Cabled Array's long-term sub-sea monitoring operations provide a modular framework capable of adapting to many applications and scales. All secondary infrastructure equipment, including cables up to 5 km, were deployed by a work class ROV and configured to fit multiple site geometries and environments, from soft sediments to volcanic crust. Seafloor nodes, or junction boxes, deliver up to 200 Watts to each of 8 instrument ports, and can be daisy-chained for expansion. Real-time controllable winched profilers routinely perform multiple 200 m vertical profiles daily, and can be docked as needed to accommodate operations in the water column above. A 3500-meter rated wire-crawling profiler samples the entire water column and recharges at a cabled seafloor docking station. While each system is tailored to its specific mission, all components of the secondary infrastructure: 1) enable remote shore-based operation of deployed equipment, 2) allow for real or near-real time data collection and system control, and 3) are synchronized to a GPS-based clock. These key attributes of interactive observatory-class systems unlock several possibilities for subsea systems, including immediate responses to detected events, accurate time-based comparisons of spatially-varying data sets, synchronized operations over an extended area, and shore-based control of remote resident infrastructure.