  Low gain avalanche detectors (LGADs) deliver excellent timing resolution,
which can mitigate mis-assignment of vertices associated with pileup at the
High Luminosity LHC and other future hadron colliders. The most highly
irradiated LGADs will be subject to $2.5 \times10^{15} \mathrm{n}_\mathrm{eq}
\mathrm{cm}^{-2}$ of hadronic fluence during HL-LHC operation; their
performance must tolerate this. Hamamatsu Photonics K.K. and Fondazione Bruno
Kessler LGADs have been irradiated with 400 and 500 MeV protons respectively in
several steps up to $1.5 \times10^{15} \mathrm{n}_\mathrm{eq}
\mathrm{cm}^{-2}$. Measurements of the acceptor removal constants of the gain
layers, evolution of the timing resolution and charge collection with damage,
and inter-channel isolation characteristics, for a variety of design options,
are presented here.
