The soldier in charge would command, after each firing, that the rank on the scaffold step down and be replaced by the rank that had just reloaded, thus alternating ranks and sustaining the rifle fire.
( ( ( The soldier ) ( in charge ) ) ( ( would ( ( ( ( ( ( command , ) ( after ( each firing ) ) ) , ) ( that ( ( ( the rank ) ( on ( the ( scaffold step ) ) ) ) down ) ) ) and ) ( be ( replaced ( by ( ( the rank ) ( that ( had ( just ( ( reloaded , ) ( ( ( thus ( alternating ranks ) ) and ) ( sustaining ( the ( rifle fire ) ) ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (NN soldier)) (PP (IN in) (NP (NN charge)))) (VP (MD would) (VP (VP (VB command) (, ,) (PP (IN after) (NP (DT each) (NN firing))) (, ,) (SBAR (IN that) (S (NP (NP (DT the) (NN rank)) (PP (IN on) (NP (DT the) (JJ scaffold) (NN step)))) (ADJP (RB down))))) (CC and) (VP (VB be) (VP (VBN replaced) (PP (IN by) (NP (NP (DT the) (NN rank)) (SBAR (WHNP (WDT that)) (S (VP (VBD had) (VP (ADVP (RB just)) (VBN reloaded) (, ,) (S (VP (VP (ADVP (RB thus)) (VBG alternating) (NP (NNS ranks))) (CC and) (VP (VBG sustaining) (NP (DT the) (NN rifle) (NN fire))))))))))))))) (. .)))
This system does not seem like it would have worked. 
( ( This system ) ( ( ( does not ) ( seem ( like ( it ( would ( have worked ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT This) (NN system)) (VP (VBZ does) (RB not) (VP (VB seem) (SBAR (IN like) (S (NP (PRP it)) (VP (MD would) (VP (VB have) (VP (VBN worked)))))))) (. .)))