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Low-frequency radio continuum studies of star-forming edge-on galaxies canhelp to further understand how cosmic-ray electrons (CRe) propagate through theinterstellar medium into the halo and how this is affected by energy losses andmagnetic fields. Observations with the Very Large Array (VLA) from ContinuumHaloes in Nearby Galaxies - an EVLA Survey (CHANG-ES) are combined with thosewith the LOw Frequency ARray (LOFAR) from the LOFAR Two-metre Sky Survey (LoTSS) to identify the prevailing mode of cosmic-ray transport in the edge-on spiralgalaxy NGC 3556. We mapped the radio spectral index, magnetic field strength,and orientation using VLA 1.5 and 6 GHz and LOFAR 144 MHz data, and we fit 1Dcosmic-ray propagation models to these maps using Spinnaker (Spectral IndexNumerical Analysis of K(c)osmic-ray electron radio emission) and itsinteractive wrapper Spinteractive. We find that the spectral index in thegalactic midplane is, as expected for young CRe, alpha ~ -0.7 and steepenstowards the halo of the galaxy as a consequence of spectral ageing. Theintensity scale heights are about 1.4 and 1.9 kpc for the thin disc, and 3.3and 5.9 kpc for the thick disc at 1.5 GHz and 144 MHz, respectively. While purediffusion cannot explain our data, advection can, particularly if we assume alinearly accelerating wind. Our best-fitting model has an initial speed of 123km s^-1 in the galactic midplane and reaches the escape velocity at heightsbetween 5 kpc and 15 kpc above the disc, depending on the assumed dark matterhalo of the galaxy. This galactic wind scenario is corroborated by theexistence of vertical filaments seen both in the radio continuum and in H alphain the disc-halo interface and of a large-scale reservoir of hot, X-rayemitting gas in the halo. Radio haloes show the existence of galactic winds,possibly driven by cosmic rays, in typical star-forming spiral galaxies.

CHANG-ES XII: A LOFAR and VLA view of the edge-on star-forming galaxy NGC 3556