Transparent transmission control protocol (TCP) acceleration is a technique to increase TCP throughput without requiring any changes in end-system TCP implementations. By intercepting and relaying TCP connections inside the network, long end-to-end feedback control loops can be broken into several smaller control loops. This decrease in feedback delay allows accelerated TCP flows to react more quickly to packet loss and thus achieve higher throughput performance. Such TCP acceleration can be implemented on network processors, which are increasingly deployed in modern router systems. In our paper, we describe the functionality of transparent TCP acceleration in detail. Through simulation experiments, we quantify the benefits of TCP acceleration in a broad range of scenarios including flow-control bound and congestion-control bound connections. We study accelerator performance issues on an implementation based on the Intel IXP2350 network processor. Finally, we discuss a number of practical deployment issues and show that TCP acceleration can lead to higher system-wide utilization of link bandwidth.