  Existing chain-based rotating-leader BFT SMR protocols for the partially
synchronous network model with constant commit latencies incur block periods of
at least $2\delta$ (where $\delta$ is the message transmission latency). While
a protocol with a block period of $\delta$ exists under the synchronous model,
its commit latency is linear in the size of the system.
  To close this gap, we present the first chain-based BFT SMR protocols with
$\delta$ delay between the proposals of consecutive honest leaders and commit
latencies of $3\delta$. We present three protocols for the partially
synchronous model under different notions of optimistic responsiveness, two of
which implement pipelining. All of our protocols achieve reorg resilience and
two have short view lengths; properties that many existing chain-based BFT SMR
protocols lack. We present an evaluation of our protocols in a wide-area
network wherein they demonstrate significant increases in throughput and
reductions in latency compared to the state-of-the-art, Jolteon. Our results
also demonstrate that techniques commonly employed to reduce communication
complexity$\unicode{x2014}$such as vote-pipelining and the use of designated
vote-aggregators$\unicode{x2014}$actually reduce practical performance in many
settings.
