In this paper, we prove that a wide class of distributed control
problems subject to communication and propagation delays are
equivalent to convex optimization problems. The results hold in
both continuous and discrete time, for both stable and unstable
systems. A specific example is formation flight, where each aircraft
has its own controller, and the effects of an aircraft's control
actions propagate to neighboring aircraft with a delay inversely
proportional to the speed of sound. Here each controller may
transmit sensor measurements from its aircraft to neighboring
aircraft with an associated communication delay, and a consequence
of these results is that if the communication delay is less than this
propagation delay, then norm-optimal controllers may be found via
convex programming.