the drawing arm 49 is mounted on rod 50 which is bolted at 51 and 52 within a slide means on plate 48 to hold the arm 49 in fixed relation to the attachment in use the pusher foot may be used as a stop against which the boom may thrust to push the support vehicle forward as the trench progresses in steps in fig3 the end sprocket 19 is mounted telescopically at 26 on the end of support frame 14 so as to enable dismantling the sprocket is allowed to telescope inwardly and as seen in fig7 support frame 14 may carry a threaded means 53 by which an outward thrust may be applied to the sprocket to tension it and bolt holes may be provided to enable it to be fixed in place where the length of the chain digger attachment is greater than the vehicle width so that its ends project beyond the vehicle sides when in the position of fig2 the length might be shortened by collapsing the sprocket 19 inwardly to enable an easy adjustable operation a ram may be fitted between the support frame 14 and the sprocket mount so as to move it in either of the telescopic directions in fig8 and 9 is shown a more developed chain digger attachment wherein.