ABSTRACT We present new high-resolution and high-sensitivity studies of the jets in the WAT source 3C 465, using deep transverse-resolved radio observations from e-MERLIN, and with complementary observations from the Very Large Array (VLA). We derive a lower limit βj = (νj/c) ≳ 0.5 for the jet speed, and an upper limit $\theta _{\rm j}\, \lesssim$ 61° for the jet angle to the line of sight. The jet spectral index (α, defined in the sense S ∝ να) is fairly constant (<αjet > = − 0.7), and spectral flattening within 4.4 kpc of the core coincides with bright knots and is consistent with the site of X-ray particle acceleration at the base of the radio jet found in previous studies. There is little difference between the spectra of the two hotspot components, plausibly indicating that electron populations of the same properties are injected there. The north-west (NW) and south-east (SE) plumes are approximately homologous structures, with variations in mass injection and propagation in external pressure and density gradients in the two regions plausibly accounting for the slightly steeper spectrum in the NW plume, <αNWp> = −1.43 compared with the SE plume, <αSEp> = −1.38. Our synchrotron lifetime model supports plausible reacceleration of particles within the plume materials. Overall, our results show that the first-order Fermi process at mildly relativistic and non-relativistic shocks is the most likely acceleration mechanism at play in 3C 465 and distinguish differences between the acceleration at $β _{\rm j}\, \gt $ 0.5 and $β _{\rm j}\, \lt $ 0.5. The former case can accelerate electrons to higher Lorentz factors.